Do actually exist a website, page (even a section in Bscscan, Etherscan) where I can track the supply of a certain token and figure out how it changed during the existence of the token?
I mean like the "historical data" section in Coinmarketcap.
It depends on why you need this information.
If you want to invest in a project and make calculations on the number of tokens available in circulation, then you need to study the project in more detail. I have come across incorrect data on Coinmarketcap, because many projects use vesting and some projects do not have complete data on the distribution of system tokens.