It is giving me choice paralysis, last week I made a mental graph of the ones I wanted and went over all node pairs choose 2, now it's down to waiting for a fall M5 Mac mini paired with either: a MacBook Neo, or an iPad Air 13"; both options are very attractive for my intended usage though the latter seems higher risk since I've never used a 13 inch tablet before.
The iPad gives you touch interaction, hand-held operation, a higher quality (albeit smaller) display, and a more resilient operating system (albeit managed).
The Neo gives you a real keyboard, a bigger screen, and unified UX/software support with your desktop computer.
But are you sure you need two devices? Why not just get a MacBook Air (with the same spec as your proposed Mac mini) along with a USB-C dock accessory to connect charging/keyboard/mouse/video with a single cable? Also don't underestimate the value of having a battery in your "desktop" computer. It's a free UPS.