If you are a “US Person” you may find it impossible to invest, or deal with certain financial institutions and products at all.
I live in the Netherlands. I will face restrictions with my earned pension compared to non-US persons. I am forbidden to use stock trading services like DeGiro. I am not allowed to buy or sell Bitcoin. Just some examples…read the T&Cs of practically any financial-related service and there is a prohibition on US persons.
There’s nothing illegal, of course, it’s simply that the vast majority of these institutions can’t be bothered to deal with the nightmare of compliance that is serving “US Persons.” It’s easier just to ban them.
Fortunately, my bank is used to dealing with international clients and they still welcome me as a client. I see in other countries Americans have it much more difficult. I was even allowed to open an investment account! It’s far from ideal, and I had to commit to selling off everything should I leave the country, but it’s better than nothing..