There wasn't anything particularly difficult to learn for the purpose of just maintaining and adding simple code that is required to keep up with banking regula

There wasn't anything particularly difficult to learn for the purpose of just maintaining and adding simple code that is required to keep up with banking regulations in France, so yes my employer gave me some documents and left me to train alone for 1-2 weeks, learned everything I mentioned, and also the coding process and specificities required by the client (code standards, like GOTOs were of course forbidden, you had to give proper names to variables, reuse existing SQL statements and extend them if needed), as well as how to document the tests and deploy to staging, production etc. And technically the access we had to the mainframe was the 3270 sessions we used to code, launched on a modern PC connected to a secure VPN connection to the mainframe. Using F7-F8 to scroll code was awful, and having only a single screen to switch back and forth when debugging CICS was awful but doable. I wish we could have had access to modern ways of coding COBOL with real IDEs with syntax highlighting done locally, and then transmitted to the MF when you save. Never tried that, and I guess I'll never need to anymore.