This started happening a few months ago, I would be minding my own Ubuntu business and then suddenly I can’t left click.
After much digging and stupid AI querying, I added something to disabled power management to my boot sequence. That seems to minimize the problems but I still get the problem every 5 minutes or so.
To temporarily fix the problem I Ctrl-alt F3 then F2 to come back to. GNOME.
I tried with a mint usb and I got the same problem. I thought it was then maybe a mouse problem but the pointer does the same no matter what mouse I use and every mouse I tested worked fine on another Ubuntu of the same release. So I think maybe it is some sort of hardware and driver combination and to power management.
I see lots of posts of past years but nothing more recently, but no real solutions or explanations for what might be happening.
Okay looks like a start up script will be the thing to do next.
Google “<your bootloader> add kernel parameter”. Likely Grub in your case.
Although this boot parameter is merely a workaround. I’ve had some issues with the flat metallic Kinston thumbdrives getting filesystem corruption because they overheat and quickly dis/reconnect even with working powersaving. Not that this must happen to you, but all i’m saying is that you still better find the root cause or get another mouse.