I had foot issues riding. I did what you did eliminated and compared between different bikes and shoes, but always same pedals. It was related to heat and how long I rode no matter what shoes or bike I was riding. I would take my feet out of my shoes and ride with them on top. My fitter tried a number of things, but no matter what when I rode long and it was hot my feet would act up.

I ended up getting custom bike shoes that helped some but by the time I got my shoes I had other health problems so am not training like I did.

Have you work with a fitter? Good luck!

I think the key here is that it is only hot rides.
You foot expands in the heat and your shoes are not allowing them.
Probably find that the toebox is too narrow for you when it is warm.

For years I assumed that sporadic foot pain during long rides was simply an unavoidable side effect of spending hours wearing shoes with a rigid base. Then about 5 years ago I was in need of some new bike shoes and decided to treat myself and go to a shop that specialises in sports footwear. Ended up spending about twice what I'd expected and coming out with a lovely pair of Sidi shoes with a custom moulded footbed. I have to say they exceeded all my expectations. Not only are they incredibly comfortable and haven't had any pain or hotspots from them, they've also helped manage a niggling knee problem that used to occur when I was doing high mileage on the bike and which I suspect was due to my foot alignment and/or poor form on rides where I was compensating for foot pain. And I think there's a performance benefit from having a more even distribution of force across the whole sole of the foot when I'm pedalling, though this might just be psychological i.e. the pain in my feet is no longer acting as a disincentive to applying more force.

For context, I do have fairly unusual feet - very high arches, pretty wide, one foot is a size longer than the other, but the foot which is shorter is also a size wider! But foot discomfort/pain does seem to be a common theme amongst many cyclists, and given the thousands that many of us spend on fancy bikes it seems crazy not to spend a few hundreds to have comfortable feet. I'd strongly recommend getting your feet properly measured and sized up and making sure that you have shoes which work well with your foot shape. And also trying different footbeds - you don't need to go full custom, there are some good intermediate options out there. I find it interesting that this sort of approach still seems relatively unusual in cycling, when in skiing (another sport where foot discomfort can be a common feature) you'd hardly find anybody buying boots without getting professional advice and fitting.

Where is the exact location of the foot pain?

As mentioned, feet swell, especially when temps rise. Usually a shoe with wider toe box will help. However, knowing the exact source and location of pain can also help with diagnosis and additional solution(s).