You got a lot of exotic suggestions, I'll give one closer to normal: Perixx Periboard 535. Split (though non-adjustable), low profile mechanical switches with three options, three tilting levels, wired or wireless, with or without numpad. And has function keys. Also quite cheap.
I got the wired option with tactile brown switches and numpad, and I've been happy with this. I was looking for a replacement for MS Sculpt and didn't want one of the wild models, this finally ticked all the boxes.
Seconded. They're pretty good and I've found them a decent replacement for the MS Ergonomic 4000 keyboards that I used to use. Full size keyboard with keys in the normal places, reverse tilt, manageable F lock, and a cable to connect it to your computer.
I've got one with clicky blue switches, which is fun to type on but a bit loud, and one with silent red switches, which is pleasant to use but the key activation is perhaps a bit too light. I sometimes find myself pressing the keys when I thought I was just hovering my fingers.
The folding stands are a weak point. The MS 4000/Sculpt sort of design, whereby the riser is a solid piece of plastic that the keyboard rests on, is much better.
I like the stands. I need two different levels of tilt, full negative for the sitting position and the mid level for standing. It's really easy to switch between the levels so it fits well my use case.
I got the wired option with tactile brown switches and numpad, and I've been happy with this. I was looking for a replacement for MS Sculpt and didn't want one of the wild models, this finally ticked all the boxes.
https://perixx.com/products/periboard-535
DE: https://www.amazon.de/dp/B0BZZJH9W2
US: https://www.amazon.com/dp/B0BLT4HDPR