How can a non us resident living outside the US, build credit?

I've studied in the US and lived there for a while before moving back to my country. I have an SSN, a US bank account and spend considerable money in the US. I would assume this would contribute to some credit building, but I always new it didn't bc there are a limited number of ways to become credit visible, such as being grandfathered in, or paying your rent and bills, etc. Is there another way for a nomad to benefit from US credit?

I ask this because I just found https://extra.app and I don't know if it's legit or a $7/month scam.