A citizen of the US can't avoid federal taxes anywhere

Sure they can. The first $107,600 of earnings, can be excluded from Federal Income Taxes. If you live in a foreign country. Look up the foreign earned income exclusion.

Not true! Google "puerto rico federal income tax" if you don't believe me.

https://www.forbes.com/sites/robertwood/2019/09/09/move-to-p...

(Despite saying "not exactly" in the title, it is in fact exactly that. Read the details. PR residents don't pay federal income tax. There's just some caveats if you're trying to move there as a tax dodge.)

Only if your source of income is from Puerto Rico.

https://www.irs.gov/taxtopics/tc901

>> If you're a bona fide resident of Puerto Rico during the entire tax year, you generally aren't required to file a U.S. federal income tax return if your only income is from sources within Puerto Rico.

I thought that applies only to non-US citizen Puerto Rico residents. Seems like you're right, thanks for correction!

Well Puerto Rican born residents are US citizens. The IRS makes it understandably difficult to change your residence to PR as a tax dodge though.

Assuming you're not working a multi national corp that has branches in the US (and therefore reports to the irs), I can't imagine hiding income abroad is all that difficult with a few shell LLC's and trusts.

That's evading taxes, not avoiding taxes (legal distinction).