Wi-Fi keeps disconnecting

[TheDead]

I think you meant WPA2-PSK and not WPA3-PSK as that is not an option.
As for the router, it was given with my Wi-Fi setup and belongs to my ISP. So, I don't know what model it is or which company it belongs to. But most probably it is not that old as I got the new Wi-Fi setup few months ago.

Yeah, sorry WPA2, that was a typo.
Indeed, if the rooter is newer it has less chances to be the culprit, if you have a chance though, check the back or under for a P,N or Model#.
But, I also though of something, if could be that the Wi-Fi antenna is loose and randomly disconnect (?)... but this would show in the Wi-Fi signal strengh.
Also, it would be some bad luck that this happaned when you changed OS... but still.

Another, other thing : Try using 2.4GHz and not 5GHz, it usually has better signal. But slower though...