I’m in a similar situation as kszaf. Running FR 11.24 and have 5 .NET CORE and ASP .NET CORE installs of version 2.1.xx. Our vulnerability scanner (Qualys) is showing them as critical vulnerabilities, so I went ahead and uninstalled them since it sounds like 11.24 should support 3.1.x.
Rebooted and couldn’t access the Web Console. Installed the .NET 2.1.30 Hosting Bundle and the Web Console works again. I’ll probably put in a support ticket on Monday to see about how to remove those older versions properly. The screenshot shows the ones I tried removing.