Upgrading from 3.6.5 to latest version 4: all my files now show as HTML


I started using Jupyter Lab by installing Jupyter Lab 3.6.5 on my MacBook Pro, created some material for a course I am building and everything was working a-ok. I upgraded to version 4 via pip and nothing works anymore… All my files are showing as HTML code and I lost all markdown as well as all code :frowning: Downgrading to version 3.6.5 fixes this.

What is going wrong?

Best regards