The 2 main issues which are troublesome if you do not detach fully from the USA , is maintaining a phone number for 2 factor authentication and whatever comes next , and maintaining your brokerge account.

I see Tello recommended as explicitly allowing expat customers, and it's cheap - added a Tello SIM and text-only plan in preparation for departure to Portugal next month. Will keep my Mint account open at least until renewal later this year - it seems to work fine with WiFi calling / texting.

Citi, Schwab, and IBKR all allow expat accounts AFAIK. I have opened accounts with each and plan to move all my remaining US equities into those before I've been overseas long enough to trigger shutdowns from others. I realize a lot of expats maintain a US mailing address (n.b. forwarding services will not work, in general) and that may work for a while, but expect that it will be found out at the most inconvenient time and would rather not deal with having accounts shutdown out of the blue.