For fun: Nim or any modern Lisp.
For profit: COBOL.
For profit: COBOL.
A quick search for COBOL resources yielded https://github.com/openmainframeproject/cobol-programming-co... , so it seems possible to learn without access to the hardware.
As far as I know, practically there are no COBOL jobs around me anymore. Big established institutions like telco and bank usually use Java. On the other side, the younger kids usually prefer something like NodeJS or Go.
There appears to be an active community around it, and I'm sure getting help in an apprenticeship sort of way is possible. Again, we're talking about a niche language, so you can't expect the same level of accessibility as NodeJS or Go.
As for finding jobs, they're probably few and far between, but appear to be well paid from what I've heard. Places that need COBOL programmers will announce it, opportunities will likely come up from other contacts in the community, and cold contacting companies you know are using it is always an option.