blackrabbit1, it is true that some countries offer citizenship, residency or immigration by investment, but I do not see any country except Antigua and Barbuda, and Vanuatu to accept
BTC as a means of payment for that service.
However this should not be a problem, you just need to sell
BTC and then invest fiat. I think these two countries will also carry out certain checks before allowing payment in cryptocurrency, otherwise many would take advantage of paying in crypto - but you will always have to prove the origin of money, regardless of which way to pay.
I also advise you to check all well, and not to trust some agents who offer visa services you will lost money and visa.
All you need to know is presented on this site :
Golden Visas