A on of insurance companies, banks, telcos, airlines and old government systems for anything related to healthcare and taxes still use it and it's not all IBM Mainframes. I think IKEA just recently migrated away from it but a lot of companies with old inventory systems still do use COBOL.
The language is easy, systems and products gigantic, your mentors write their code (incl. Java) in a 55x132 char terminal and sometimes there is even more than absolutely no documentation!
It's fun but I'll probably want to do something more modern for a while before maybe returning to the old systems.
For anyone interested to learn, I've recommended think Jan Sądek's mainframe playground before ( https://mainframeplayground.neocities.org/ ).
Keep an eye on IBM's "Master the Mainframe" and hobbyist licenses for OpenVMS. I found setting up GnuCOBOL in a nice way was too much of a hassle to recommend.