Since tha last Premiere update I get a System Compatibility report about OS (no more supported) although I have the last updates installed

if you are still on Win10, it’s because that OS is no longer fully supported by Microsoft, only some security updates if you have paid extra for this to Microsoft.

Most software vendors do not continue to support dead OS versions … which can be a right pain, but is pretty common.

What operating system and version?

What Premiere version and build number?