Left mouse button disabled — does this sound like an online attack?

At the parents' yesterday, trying to get their computer sorted out, and something odd happened.

After one of the restarts, the left button on the mouse stopped working. Couldn't click on anything. Had to restart it to get it working, and I did that by right-clicking menu items, and pressing return to start the reboot.

Why do I suspect a malware attack? Because the same thing happened to my laptop, which gets used VERY differently. The current version of Ventura and their home network were the only things in common.

What do I install on their computer, which I've nicknamed "The [woman of ill repute] of Publisher's Clearing House", to block against malicious adware or other things which an indiscriminate contest-enterer might easily stumble into? Basically my father is getting stupid all over that machine, and I need a way to StupidGard it.