(Why) did the PRC not [ever] recognize the incorporation of the Baltic states into the USSR?

The PRC did not recognize de iure Soviet annexation but did recognize de facto Soviet rule, according to two sources:

Lauri Mälksoo (2003, 2022 2e, p. 102):

The second and probably numerically the biggest group of Western States, never accorded de iure recognition to the Soviet annexation. However, they did recognize Soviet rule de facto. This group of States included Australia, Belgium, Brasil, Canada, Chile, China, Colombia, ...

Estonia, 1940-1945: Reports of the Estonian International Commission for the Investigation of Crimes Against Humanity (2006, p. 198):

The second group includes those countries, which did not recognise the occupation of the Baltic State de jure, but recognised Soviet rule in the Baltic States de facto. These countries are Australia, Belgium, Brazil, Canada, Chile, China, Iceland ...

The following quotes from Peking Review strongly suggest full recognition of Soviet annexation of the Baltic states (at least by the respective writers but not necessarily by the government):

1960-08-12 (p. 17, translated from Hongqi):

Recently, U.S. Secretary of State Herter issued a provocative statement propagating the illusion that the three Soviet Baltic republics of Lithuania, Latvia and Estonia would one day "again enjoy national independence."

1960-08-16 (p. 10, translated from Renmin Ribao, 1960-08-13):

China is a socialist state. Like all socialist states, China will absolutely not permit aggression against other countries. At the same time, it will absolutely not permit other countries to encroach on its territory and sovereignty. The Soviet people are firmly opposed to the aggressive designs or U.S. imperialism in clamouring for the "liberation" of the three Union Republics of Estonia, Latvia and Lithuania. The Polish people are firmly opposed to the mad plan of the U.S.-backed West German militarists to "recover" the western territory of Poland.

1967-09-01 (p. 33):

in the past two years, many collective and state farms in the Russian S.F.S.R., the Moldavian and other republics of the Soviet Union have, for the sake of profit, arbitrarily reduced the acreage under crops which are less profitable ... In the Latvian Republic, many collective farms have set up their own shops or joint-stock companies to make fat profits by selling their agricultural and subsidiary products at open market prices.

1967-11-03 (p. 33):

Jazz festivals have been held every year in the Soviet Union since Brezhnev and Kosygin came to power. This year, one took place in Tallinn, capital of the Union Republic of Estonia, lasting four days.

Most countries, unless they were either outright allied or outright opposed to the USSR, were simply not very interested in the Baltics and so adopted the middle position of de facto recognition but not de iure recognition. (And such countries often never issued any explicit statement on the legal status of the Baltic states. I believe this is true of the PRC.)

Vilnis Šveics (1978):

One of the most spectacular developments concerning the Baltic States in the last ten years is the interest of the People's Republic of China in the fate of the Estonians, Latvians, and Lithuanians.

This is a new and significant trend. For the first time in history a country situated in Eastern Asia shows consistent concern for the situation and events in the Baltic area. ...

The People's Republic of China (P.R.C.) was proclaimed in 1949. It is a newcomer in world politics. Yet, despite an often predominant introversion and concern with local issues, the Peking leadership has developed an impressive international influence.

In retrospect, it is clear that China's attention gradually turned to the Baltic nations as a result of the Russo-Chinese conflict and the consequent interest of the People's Republic in the fate of the East European countries and European security. It was also influeced [sic] by Peking's concern with its own internal nationality areas. ...

It is interesting to note that in their references to the Baltic countries the Chinese publications never describe them as "Soviet" Estonia, Latvia, Lithuania, nor as "Soviet republics", but simply as "Estonia, Latvia, Lithuania," or collectively as the "Baltic countries" or "Baltic nations," even "Baltic states."

Perhaps not a complete answer, but snippets of information can be found in this free book: Illegal Annexation and State Continuity, specifically covering the annexation of the Baltic states.

Regarding the position of China vis-à-vis the annexation (pp. 102-103):

The second, and probably numerically the biggest group of States, never accorded de iure recognition to Soviet annexation while recognizing it de facto. This group of States included Australia, Belgium, Brasil, Canada,144 Chile, China, Colombia, Costa Rica, Denmark, Ecuador, France,145 the Federal Republic of Germany, Greece, Guatemala, Luxemburg, Malta, Mexico, Norway, Paraguay, Portugal, Switzerland, Turkey, Venezuela, the UK,147 Uruguay and Yugoslavia. For instance, the British Embassy in Moscow did not engage in official communication with the State organs in the Soviet Baltic republics.

The Stimson doctrine, opposing the recognition of the annexation, was apparently explicitly designed to make such moves difficult for China (pp: 98-99)

The doctrine of non-recognition of the fruits of aggression was formulated by the US Secretary of State, Henry L. Stimson, on the occasion of Japanese aggression in Manchuria in 1932.128 The last sentence of the US diplomatic note served as the basis of the Stimson doctrine:

and that it (i.e. the US government) does not intend to recognize any situation, treaty or agreement which may be brought about by means contrary to the covenants and obligations of the Pact of Paris of August 27, 1928, to which treaty both China and Japan, as well as the United States, are parties.

Note though that the treaty predates the Communist revolution in China (1949).

Finally,

Germany has recognized the identity of the Baltic States with the pre-World War II Baltic States, yet it has announced that it prefers not to reinforce pre-World War II bilateral treaties with those States.36

where

36 A similar position was taken by Japan, Italy and China. Possibly, it is also due to fundamental political changes that have taken place in those countries, i.e. not only in the Baltic republics.

I'd contend that the wiki page is - most likely - simply wrong about the facts. It does seem to be the case, in my experience, that long list articles are of lower quality than regular ones and often get their references wrong.

Indeed, there are 3 references provided at the moment:

[49][50][59]

[49] - Mälksoo, Lauri (2003). Illegal Annexation and State Continuity: The Case of the Incorporation of the Baltic States by the USSR. Leiden – Boston: Brill. ISBN 90-411-2177-3.

[50] - Toomas Hiio (2006). "Legal continuation of the Republic of Estonia and the policies of non-recognition". Estonia 1940-1945: Reports of the Estonian International Commission for Investigation of Crimes Against Humanity. Tallinn. pp. 195–198.

[59] - Lawrence Juda, United States' nonrecognition of the Soviet Union's annexation of the Baltic States: Politics and law, Journal of Baltic Studies, Volume 6, Issue 4 Winter 1975, pages 272–290

Now, [49] and [50] do not seem readily accessible but [59] is a 1975 paper one can download in a moment, which I did.

And it turns out that, as expected, the wiki editor totally misunderstood Juda's paper. The only time "China" appears in the paper is the very first paragraph:

Each state desires its claim to authority over all its territories to be recognized as legitimate by other states. It is well known that the People's Republic of China has challenged the legitimacy of Soviet control of portions of the Soviet Union along their long common frontier. Much less well known is the situation with respect to the Baltic States, the incorporation of which into the Soviet Union has still not been recognized by the United States. This article will examine the status of the Baltic States from the perspective of the United States government, noting the causes and some of the consequences of such nonrecognition.

Clearly, all Juda meant to say is that the PRC had territorial disputes with the Soviet Union with respect to their shared border. As is well-known they even went to a nano-war over said disputes. But the rest of the paper is about the US stance and China does not figure in it.