How does Protestantism defend the adoption of practices and beliefs not found in the Bible?

There are many practices in different protestant denominations that are observed, and defended, but not expressly commanded in scripture.

But to answer your question, in these instances, it is most often a cultural issue or cultural practice, but it is not an issue which is strictly forbidden in scripture, or in other cases, scripture is silent on the issue.

I'll give several examples from different cultures.

In Russia, in Protestant churches, it is common for men to sit on one side and women on the other.

It's also common in Evangelical churches for men to greet other men with a kiss and women to also greet other women with a kiss. This is a product of Slavic tradition and is not expressly forbidden.

Another example from churches in Russia and Ukraine - women may pray in public, but a man should end the prayer. This is not supported by scripture, but is totally a cultural issue. They defend this practice by using the verse that man has authority over women. Another example is that in Danish Evangelical Churches, and Evangelical Churches in Poland, it is common practice to not allow someone to take communion unless that person has been baptized. Again, this is a cultural issue, and there is nothing in scripture anywhere that says a person has to have been baptized to receive communion - but they defend this, with the scriptural idea that baptism is an act of obedience and public declaration of faith, and communion is another part of identifying with the body of Christ. It's a stretch for sure.

In the same way - many protestant churches around the world ban women from being a pastor, or holding an official role as a pastor, or an elder, or where they teach doctrine to men. Some even go farther and do not allow women to teach Sunday school, or lead Bible study groups where men are present. It's from the words of Paul that women should be silent in churches.

Another example is that most churches in Europe use wine for communion, but they use regular bread. Not unleavened Matzo. Is it Biblical? - No. Is it how Christ celebrated Passover? - No. But they also see that the elements are symbolic, and they don't save a person, and in some places in the world, grape juice is not available, so it's legalistic to demand Christians use elements that aren't available.

As for the example of meeting on Sunday, this is a widely - practiced custom around the world, but the truth is that the Sabbath always was and is still on Saturday.

The early church was meeting on Sunday, and we see this in Acts and the Epistles from Paul.

Paul also explicitly said to the mixed - Jewish and Gentile churches in the early church that we should not judge each other based on which day they observe to worship. Again, there is no explicit scripture against it.

In the cases where scripture is clear - or it is a major issue of doctrine, then Protestants hold scripture as the final authority - and it takes precedent over tradition. That is why Protestants believe in the Virgin birth - because it is clearly in scripture, but reject the concept that Mary was sinless.

It is explicitly clear in scripture - in more than one place that all mankind- every man and every woman is sinful -so scripture takes priority over tradition.

Scripture also says clearly that Christ is our mediator and that He is our high priest. Scripture also says that Peter was married, and marriage was instituted by God, and so the notion of making priests be celibate is not supported by scripture and many Catholics around the world see this as controversial issue. There is no explicit ban in scripture, and even in the Catholic church, priests were married and had families until about the 11th century. https://catholicstraightanswers.com/why-does-the-church-mandate-that-priests-be-celibate/

https://historynewsnetwork.org/article/696 "The practice of priestly celibacy began to spread in the Western Church in the early Middle Ages. In the early 11th century Pope Benedict VIII responded to the decline in priestly morality by issuing a rule prohibiting the children of priests from inheriting property. A few decades later Pope Gregory VII issued a decree against clerical marriages.

The Church was a thousand years old before it definitively took a stand in favor of celibacy in the twelfth century at the Second Lateran Council held in 1139, when a rule was approved forbidding priests to marry. In 1563, the Council of Trent reaffirmed the tradition of celibacy."

The Catholic Encyclopedia's article on tradition mentioned in the OP confuses itself and thus the Protestant practice and belief.

The article begins with a definition. Emphasis is mine.

The word tradition (Greek paradosis) in the ecclesiastical sense, which is the only one in which it is used here, refers sometimes to the thing (doctrine, account, or custom) transmitted from one generation to another; sometimes to the organ or mode of the transmission (kerigma ekklisiastikon, predicatio ecclesiastica).

But in its application thereof to the Protestant position (sola scriptura), it fails to identify in which sense it is using said word (tradition). The article agrees with the Protestant that there is such a thing as tradition, like Christ was born on December 25, but where it loses the argument is when it continues with that definition of tradition (custom) and applies it to Tradition or in the language of the article, revealed truth.

That "revealed truth" or Tradition with a cap T is where the Catholic and Protestant part company. For the Catholic, she believes Jesus left an unwritten, oral truth passed perfectly from one generation to the next and by which she defines her "de fide" statements. An example would be the old Bull that said outside the Catholic Church there is no salvation. Or one must believe Mary remained a virgin during and after the act of Christ's normal human birth. Or various other statements spoken as Tradition, not tradition.

These definitions of Tradition (revealed truth) are the things against which the Protestant disagreed.

So, if one keeps one's definitions consistent as one reads and understands, then one will find there is no "logical inconsistency". Essentially the "problem" was invented because the author confused between tradition and Tradition and falsely applied the latter to the former. It is called the fallacy of Equivocation.

As far as the Magisterium is concerned, a teaching authority of some type is Biblical. Paul asks are all teachers. Peter warns of false teachers. John mentions false apostles. The question is from where will the true teacher pull true information to teach? Will it be from Divine Inspiration (bible) or unwritten, oral Tradition? What will be the plumb line against which what is taught is determined true?