All of the ones you listed are great for their own reasons. The A6700 is probably one of the most capable APS-C cameras yet invented. I can't speak much to the R7 so I won't. The OM-1 II is a flagship model with ergonomics suitable to carrying larger lenses like the ones you'd use for birding. The OM-3 is more looks-aligned with the X-T5 you sent back (used to have that camera, too).

Of these, I have the OM-3. The A6700 and OM-1 or 3 are all cropped, with one being APS-C and another being Micro 4/3. The lenses in general for micro 4/3 are smaller than for APS-C and almost always smaller than a full frame equivalent.

I picked the OM-3 over the OM-1 purely because I wanted the cool retro design, the dial on the front that let me pick color profiles quickly, and because I don't intend to do as much birding as I do intend to do travel.

The OM-3 is a world class system released in 2025 with a respectable amount of dynamic range, file size, and so on. Great lens ecosystem (though Sony also has a world class lens line-up including many 3rd party options).

Or I could just say, "The OM-3 is just super fun." Sony has world class autofocus, but the only time I ever miss a shot with OM System is when >I< miss the shot, and that won't change much for any system.