Probably not a great suggestion these days. Back when I first got carpal tunnel / RSI (1995), I was using an IBM model M - which I loved the feel of. I had a dream of cutting a keyboard in two and hanging two halves off my chair so I could drop my arms to my sides and type that way.

Anyway, after trying a couple of things, Microsoft Natural (the original with backtilt) saved my programming career. I still have "weak" wrists/fingers/forearms, but it's rarely painful enough for me to have to stop working. Adding in some stretches generally makes it so I can survive.

I can type on a normal keyboard for maybe 15 minutes and maybe an hour on a laptop before I just can't anymore. I can generally go most of the day on my Microsoft Natural. Retraining from a regular keyboard layout (took typing in high school - yes, I'm ancient) wasn't hard at all - it's basically the same.

Sure, it's technically not a "split" keyboard - it's still one thing. These days, I buy used examples off ebay, usually 3 at a time, and on some, the typing action is horrible - but I still have a couple of examples that are usable. And I had to find the right ps2->usb adapters for my work setup. If I ever totally run out, my professional coding days are probably done.

Crazy suggestion, just connect two normal keyboards. Particularly if the left one is numpad-less you’ll get much of the idea for sure.

They might be a smidgeon further apart than might be ideal, there’s some ugly duplication… which happens to enforce a minimum distance… just get that shoulder opened up and start evaluating. It’s certainly likely to be more optimal than the status quo.

Might need Karabiner on macOS to keep shortcuts working.

The Keychron V10 perhaps? It has a split layout but doesn't have physically separate halves.