Again, you do not need to rewrite anything if you don't want to upgrade to .netcore/5.0 because .NET Framework is still supported and has a long lifecycle tied

Again, you do not need to rewrite anything if you don't want to upgrade to .netcore/5.0 because .NET Framework is still supported and has a long lifecycle tied to Windows itself. You can even write C# 1.0 code and it will still compile and run today without any issue. Do you expect software to stand still for decades? Please show which other language stack comes anywhere close to this kind of stability because several of them (go, nodejs, rust) didn't even exist when .NET was first released and running critical systems in major companies. You can still find COBOL and Fortran jobs if you want to avoid anything new, no need to complain about the industry moving on.