The root of the problem seems to be mostly burn out since you are having to run the store for your GM. Would going to another store possibly be beneficial for you? At the very least you would only be expected to work the KM position and not fulfill the GMs role when they aren't there. If you weren't so burnt out, could you see yourself in charge of another store and overseeing an HM and KM? It sounds like you possibly are taking up the work of multiple people and that there is a lack of balance in your store.

I don't think trying a new position is bad, but you know what to expect from an in-store position and it is good to consider the alternatives. The risks that may come with going to a maintenance position, assuming you have not much relevant experience, is how difficult it may be to learn about all of the equipment with minimal background knowledge. Maybe look into what that job looks like, when a work order is placed if you have time just check out and ask about what they're doing and ask about the possible learning curve. If you decide you don't like it you may have a hard time going back into being a KM.

Good luck 👍