This also is a major sticking point for non-Catholic Christians. Not only that but some claim the Catholic Church established belief in Purtgatory as a money-making scheme. Purgatory has ample scriptural support noting two things: 1.) some of this is based on Sacred Tradition which Catholics deem equal in efficacy with Scripture (Sacred Tradition is treated elsewhere as its own topic); 2.) some scriptural support is reliant on the deuterocanonical books (a/k/a apocrypha)* in the Old Testament; and 3.) logic which treats all of the Bible and not cherry-picking and adding or subtracting words which alter the meaning of Scripture passages.
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*The deuterocanonical books (from the Greek meaning "belonging to the second canon") are books considered by the Catholic and Orthodox, to be canonical books of the Old Testament. These consist of seven books in the Old Testament usually omitted from Protestant bibles. Martin Luther included them and they can also be found in the first King James Version (1611) and in the first Bible ever printed, the Gutenberg Bible. In fact, these books were included in almost every Bible until the Edinburgh Committee of the British Foreign Bible Society excised them in 1825. Until then, they had been included at least in an appendix of Protestant Bibles. It is historically demonstrable that Catholics did not add the books, Protestants took them out. (1) They are: Tobias, Judith, Baruch, Ecclesiasticus, Wisdom, First and Second Machabees. (Wikipedia)

(1) Jason Evert, How to Defend the Deuterocanonicals, Catholic Answers, 9/1/2000 accessed 11/20/23, https://www.catholic.com/magazine/print-edition/how-to-defend-the-deuterocanonicals
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What does the Catholic Church teach about Purgatory? Wasn't it just a money making scheme?
By Catholic Answers
Excerpt: The Catechism of the Catholic Church defines purgatory as a “purification, so as to achieve the holiness necessary to enter the joy of heaven,” which is experienced by those “who die in God’s grace and friendship, but still imperfectly purified” (CCC 1030). It notes that “this final purification of the elect . . . is entirely different from the punishment of the damned” (CCC 1031).

The purification is necessary because, as Scripture teaches, nothing unclean will enter the presence of God in heaven (Rev. 21:27) and, while we may die with our mortal sins forgiven, there can still be many impurities in us, specifically venial sins and the temporal punishment due to sins already forgiven (continued).