There is a lot of debate about that, and the best thing is to contact a tax attorney. But a lot of digital nomads in Southeast Asia are working for American clients and getting that income in under the exclusion. I’m not sure if it’s different for full time rather than contracting income.

you spoke fairly authoritatively, then hedged at the end ("almost certainly"). have you read IRS form 2555? that's probably a good place to start, as they spend a fairly large amount of time defining terms.

for all their faults, the IRS has extremely clear definitions and exceptions when it comes to foreign earned income and sequelae. while detailed and nuanced, there aren't really any gray areas that i have found.

https://www.irs.gov/pub/irs-pdf/i2555.pdf

That is what the IRS (and most tax offices in the world, such as the British HMRC or the Italian AdE) defines as "foreign source income" since the work is literally being carried out abroad. It also includes capital gains and interests arising abroad of course.