Mainframe nowadays do support modern language and modern tech stack. It's just no one willing to move on to the next stack.(or probably too expensive to) For e

Mainframe nowadays do support modern language and modern tech stack. It's just no one willing to move on to the next stack.(or probably too expensive to) For example, IBM z runs linux. Backward compatibility is one of the biggest selling point mainframes provide, you can run code written 30 years ago with all limitation and bug preserved as is. And IBM z can also run many program write for original ibm/360 unmodified. Probably many ones decided to do so.