I'm not a design person but I hear that Krita is superior free open-source alternative to Gimp.

Idk more than that honestly. I'd just recommend that before you build your skill tree out in one particular design/editing oriented program and you end up getting locked into one tool, make sure that you are very cognisant of what you're locking yourself into first.

Reskilling into a different tool isn't impossible but it can be prohibitively difficult due to a sort of sunk-cost fallacy with regards to time invested; why are you going to drop a solid 10-50 hours into learning a new tool when you can spend 20 minutes with your "native" tool to achieve the same outcome, especially when we're talking about a hobby endeavour and not a professional one?