90% of US-based Seed-level investors will not invest in a foreign entity. 90% of investors also will consider a complex corporate setup (at pre-seed) to be a big red flag - questions of IP residency, financial/taxation obstacles, lack of alignment/prioritization among founders, etc. "U.S. only" is the right choice, especially after the crypto clown show of the last six months.

There is no issue with a US entity employing a person in the UK - your citizenship is irrelevant.