Oh god I know too much about this. Long comment. Sadlol.

What kind of cast? Above or below the elbow?

I had above the elbow for 9 weeks once and below 3 times for 3-6 weeks on my right arm. Only below the elbow on my left but 5 times. My bones aren’t so good.

Above the elbow I played a lot of Warcraft 3(long time ago lol), Civ, AoE etc. Games that only required simple clicking but lots of hot keys to control. Above the elbow cast prevents a lot of you ability to rotate your arm so switching the mouse to your left doesn’t help much.

Below the elbow it depends if your thumb is immobile or not. If your thumb is free then it’s a matter of buying a cheap small mouse that will fit in your palm with the giant cast bulge. FPS and fast movements will be painful and not recommended but slower games and general use isn’t much impeded.

Immobile thumb is maybe the worst. Grab a cheap number pad and place it under your hand so you can use four fingers on the buttons. Mouse in your left hand. This severely limits what you can do with a computer.

Look up some brain exercises to ease the transition between sides of your brain and handedness. Also hold on to the skills you develop in these few weeks. Being able to work right or left hand helps with a lot of manual tasks with weird angles like using a drill under a sink or what have you.