Let's imagine whether we have reborn for uncountable times and we have met the past Buddha before.

Then we meditate the concentration meditation follow DN10 Subha Sutta, etc. in this life and start to randomly recall our past life because of the beginner's skill in Eight Vijja, DN10 AdhiPannaSikkha.

The past remembrance about the past Buddha, sanna, can appear very as photographic memory, high resolution, to the Jhana Practitioner or even normal person who has the past wholesome collection. And some of them could say "I met the Buddha". This could be real because he could have met the past Buddha before and he can use the recall skill in Eight Vijja to see his past remembrance (sanna) of the past Buddha who he really met before actually.

Great question.

Citing [2]:

As the 5th and final Buddha of our times, Maitreya's goal would be to reinstate the Dharma.

In all branches of Buddhism, Maitreya is viewed as the direct successor of Gautama Buddha.

In some Buddhist literature, such as the Amitabha Sutra and the Lotus Sutra, the being is referred to as Ajita.

Despite many individuals and religious leaders claiming to be Maitreya throughout history, all Buddhists firmly agree that these were false claims.

Taking one step back and taking a broader perspective:

Citing [1]:

Scriptures from early Indian Buddhism:

... talk about five buddhas that have existed during the current cosmological era or kalpa—a term that means an aeon, or the period from the origination to the end of the present world. The Buddha we know about, Shakyamuni Buddha, was the fourth of this group. The fifth is known as Maitreya, or the Buddha of the future.

In Theravada Buddhism:

... the tradition practiced mainly in Southeast Asia and Sri Lanka, people pay homage to 29 buddhas, most of whom existed during other kalpas, according to the scriptures.

The Mahayana Buddhist schools of East Asia and Tibet:

... know countless buddhas and bodhisattvas—awakened beings who stick around in this world in order to help others reach awakening. We see them in artworks, and their legends populate scriptures and Buddhist stories.

Not every buddha is specifically known to us. One class of enlightened beings is made up of buddhas “on their own” (in Pali and Sanskrit paccekabuddha, pratyekabuddha). These beings have achieved awakening without a teacher or guidance, and they don’t teach the path to enlightenment or have followers.

Sources:

[1]. https://tricycle.org/beginners/buddhism/are-there-other-buddhas/

[2]. https://en.m.wikipedia.org/wiki/Maitreya

[3]. Lotus Sutra, pdf: http://avalokiteshvara.net/abscI/PDF_Files_ABSCI/10SutratheUniversalGateofAvalokiteshvara.pdf

There are three types of bodies of the Buddha in Mahayana - Dharmakaya, Nirmanakaya and Sambhogakaya.

I believe that the concepts of Dharmakaya (eternal truth form) and Nirmanakaya (physical form) originated from the following sutta quote.

The Buddha downplayed the importance of his physical form and advised Ven. Vakkali to focus on the teachings, stating that when one sees the Buddha, one sees the Dharma (teachings), and when one sees the Dharma, one sees the Buddha.

In other words, the Dharma is what the Buddha stands for, and the Dharma is what the Buddha represents. The Dharma (teachings) is his eternal "form".

Vakkali: “For a long time, venerable sir, I have wanted to come to see the Blessed One, but I haven’t been fit enough to do so.”

Buddha: “Enough, Vakkali! Why do you want to see this foul body? One who sees the Dhamma (teachings) sees me; one who sees me sees the Dhamma (teachings). For in seeing the Dhamma (teachings), Vakkali, one sees me; and in seeing me, one sees the Dhamma (teachings).
Vakkali Sutta (SN 22.87)

I believe that the concept where the Nirmanakayas of all the past Buddhas emanate from one Dharmakaya originates from the following sutta quote.

It simply means that all the past and future Buddhas rediscover, understand and teach the same Dharma (teachings), because it is the natural law.

Hence their physical appearance as teachers, emanate from the Dharma (teachings) as their one eternal "form". In other words, all the Buddhas stand for the same Dharma (teachings) and all the Buddhas represent the same Dharma (teachings).

Past Buddhas,
future Buddhas,
& he who is the Buddha now,
removing the sorrow of many —

all have dwelt,
will dwell, he dwells,
revering the true Dhamma.
This, for Buddhas, is a natural law.

Therefore one who desires his own good,
aspiring for greatness,
should respect the true Dhamma,
recollecting the Buddhas' Teaching.
Garava Sutta (SN 6.2)

And what about the Sambhogakaya (enjoyment/ reward form, or perhaps inspirational form)?

I speculate that it's related to the following quote.

When one recollects the Buddha, who he was, what he achieved, what he contributed and what he stood for, that person becomes inspired and his fears dispelled. So, this inspirational mental image of the Buddha is the Buddha's inspirational "form". He can manifest in this "form" to inspire and dispel fear.

But bhikkhus, I say this: If you have gone to a forest or to the foot of a tree or to an empty hut, and fear or trepidation or terror should arise in you, on that occasion you should recollect me thus: ‘The Blessed One is an arahant, perfectly enlightened, accomplished in true knowledge and conduct, fortunate, knower of the world, unsurpassed leader of persons to be tamed, teacher of devas and humans, the Enlightened One, the Blessed One.’ For when you recollect me, bhikkhus, whatever fear or trepidation or terror you may have will be abandoned.
Dhajagga Sutta (SN 11.3)

So, you can say that this is the inspirational form of the Buddhas which bless people's minds.