I'm curious if coins obtained from all non-KYC sources of Bitcoin are equally at risk of being "flagged".
Any and all coins are at risk of being flagged by centralized exchanges. Centralized exchanges use different blockchain analysis services which have different criteria and different blacklists for which coins they will and will not accept. What is acceptable to one exchange may not be acceptable to another, and vice versa. I
previously did a quick analysis which showed one particular blockchain analysis service thought that 25% of the coins coming out of Binance should be blacklisted. You could quite easily buy all your coins through a regulated KYC exchange and find them seized when you deposit them to another regulated KYC exchange. Never mind all the other risks which come with using KYC exchanges of zero privacy, zero security, the possibility of scams, insolvencies, hacks, data leaks, etc., and the possibility the government shutdown or seize all their assets at any time.
If you are worried about your coins being seized by centralized exchanges (as you should be!), then the best course of action is not to acquiesce to their insane requirements or to change your behavior to suit them. Rather, it is to avoid using centralized exchange altogether. Bisq, AgoraDesk, and RoboSats are good exchanges to look in to instead. More available here:
https://kycnot.me/If you don't do anything illegal you don't have to worry.
Tell that to the thousands of innocent users who have had exchanges seize their "tainted" coins.