For your mouse double click issue, I have a g600 and ran into the same thing. It’s due to a teeny tiny copper plate in the switch degrading over time. I’m not confident in my soldering skills to swap out the whole switches, but I was able to buy some new switches for like $5, pop open the little plastic switch box, carefully pull out the little copper plate with tweezers, pop open the switch on my mouse, and carefully replace the little copper plate with the new one. Worked like a charm.
I think that would be more difficult because that is a different much smaller switch if I remember correctly.