There are more and more user reports that the exchanges began to freeze accounts “because some of your BTC have visited dirty addresses”. This may be as far in the past as the Binance event 5 months ago.
Thus, in practice, exchangers can freeze any amount of funds to cover cash gaps just picking up on the history of transactions of users. Think about it! A user once happened to have bought somebody’s “dirty” BTC. He brought it over on the exchange and then made long sequences of transactions with other bitcoins involved. Suddenly he gets a ban and the exchange can marinate his bitcoins for as long as it wants. It can affect everyone.
Please avoid exchanges.