Question Unity Package Manger

I recently downloaded Unity and downloaded all that was necessary for unity to Run, but for some reason whenever I try launching a project, its comes up with an error message stating that I'm missing the UPM.
I haven't deleted anything and have countlessly re-installed Unity but the same problem keeps coming up.

Windows Firewall Defender pops up with a warning about Unity and I have tried disabling and exempting Unity from Windows Firewall defender's outbound/inbound rules but that didn't seem to work.

I have installed Unity a year back but never came across the same problem (I use version 2021.3.11f1 LTS).

Has anyone got the same problem and if so, what did you do?

Many thanks.