If you look at mountain bike frames, keep in mind that you might not get the chain stay length you might want for a heavy load on the back. A shorter chainstay will push the center of gravity of your loaded rear rack further behind the rear axle, which can impair handling.

And if there is any flex in the frame, the further back that the load center of gravity is, the more that the bike will have a tail wagging the dog kind of feel.

My touring bike chainstays (three bikes) are 445, 450 and 466mm. My rando bike is 435mm and my road bike is 430mm. My errand bike is an early 90s steel frame mountain bike, the chainstay is about 425mm.

Thus, the shortest chainstay I have is an old steel mountain bike. I often load that bike down with a heavy load of groceries, from that I can say that the handling is not great with a load, but the bike cost me $5 USD at a garage sale and the grocery store is only a few miles away so I put up with the poor handling.

Your trek photo did not show fenders, so I am not sure if fenders is part of your plan or not. One more advantage of a 26 inch bike is that you are less likely to have toe overlap. All of my 700c bikes that have fenders have toe overlap. But none of my 26 inch bikes have toe overlap, even the ones that have fenders and 50 or 57mm tires do not have toe overlap. I can't say that ALL bikes fit this rule of thumb, but it might be a useful comparison if you plan to have fenders.