I’m still seeing recruiters advertise for mainframe (COBOL, CICS, CA DB2) positions with state governments, but where strong object oriented language skills (java server pages, Visual Basic. ASP, SQL Server) is also needed for GUI or mid-tier programming.
There’s one oddity in my own past learning curve. Back in the 1980s, it was easy for me to pickup mainframe IBM assembler programming working on the Chilton (Dallas) monthly billing system. That included heavy register usage and “coding out of addressability”. But in the late 1990s, early 2000’s, OOP (java, or Powerbuilder environments) were very hard to learn when I had to step into someone else’s work in maintenance mode