I know there are multiple garage threads through the years, but they all seem to focus on humidity being the issue, and I believe with my circumstances I would have a different set of issues.

Outside of the added theft risk, is there anything to worry about by keeping firearms in a safe in the garage IN ARIZONA. AZ means no humidity most of the year with a few months of like 40% (which is still relatively low). So I dont think humidity or rust is a concern (correct me if I'm wrong!) I don't remember anything metal of mine ever rusting here the entire time I've lived here haha (outside of metal outside that is exposed to things like rain obviously!)

My primary concern is it gets to 120 degrees here, so I imagine it would get very hot in the safe during the summer. I know the heat doesn't damage firearms in the short term since there have been plenty of days where my rifles are sitting out during shoots, right in the blistering sun. But I do get worried about long term effects. Especially plastics and rubbers. My black rifles are probably my least concern and I am more concerned with my LR precision rifles.

What about Ammo? I don't mean a stockpile, but I like to keep my loaded mags in the safe with guns.

What about things like backup Hard drives?

I imagine battery life in things like scopes and rangefinders will be severely effected, but thats the least biggest deal if I have to replace them every few years instead of every decade haha.

The garage is the last place I wanted to put it but the BF7250 is a BEAST and after extensive measuring, it was very impractical to put it anywhere inside. So other than "find somewhere else to put it", I am open to all comments and suggestions!

I would not think your garage gets to 120 - it's out of the sun, and cools off at night.

Any idea of how hot it does get there - maybe get a thermometer and get some data.

Here in Houston, it's often 95-100, but it doesn't that warm in the garage.

I'd wager you'd be fine - worst case, you could look at putting in a windy unit or such in your garage, that would cut the heat down on the hottest days.  In Florida a lot of garages have those to make them usable during the summer.