If you want protection for hot weather, mesh jackets are the thing.
Now they often come with one and sometimes two liners (cold/wind and/or waterproof), but IMHO you don't want either liner (or to pay for them), and you want pure mesh as opposed to just some mesh. Many partial mesh jackets are solid over the shoulders and arm tops, right where you want good cooling.
I assume you carry rain gear so see no need for extra liners for a pure mesh jacket.
Next is color, and the lighter the better (though 85% of them are pure or mostly black, which just absorbs heat). The other issue (for me) is that so many mesh have outlandish designs or brand logo stuff (just like so many full face helmets) and I don't like that either.
And most mesh jackets come full of armor and if you want the protection leave it in, but I take most of mine out (of internal pockets) so I don't look and feel like a football player, and of course this lets even more air flow through the jacket.
Look for closeouts from websellers, and it can be worth your time riding around to a few bike shops (metric dealers or aftermarket gear sellers).
My (ice cream man) pure white mesh was marked down to under a third of MSRP at a local metric dealer showroom. (First Gear or Joe rocket, can't remember). Pure mesh with no liners.
Also check here. https://www.motorcyclegear.com/street/closeouts/jackets_and_pants___mesh_/
I wear loose hi tech sweat wicking T shirts under the mesh.
Also, baggy/loose jeans up on the HWY pegs fill up with air and get rid of heat, but you still have jeans protection. Lightweight cotton pants are cooler, but the bottoms won't stay open on the hwy pegs like loose jeans will. And the cotton pants aren't much protection.
I still wear good gloves and boots as my hands and feet don't get hot.
A wet bandana around the neck is very cooling, though they don't stay wet for long. I'm not a fan of skullcaps or do-rags of any kind, but they can be soaked down too.
Finally, after riding around my area for 30 years, I have some pretty good shady rides scouted out where a good part of the ride is under trees.
I bunged up a knee a couple weeks ago and have stayed off the heavy fatgirl weaning it back to almost healthy. I was going to go for the first time today, but 90s is too much for me. I didn't get up early enough.
No I don't have any ice cream for sale!!
(and white is HI VIZ)
