I'm able to compile Add-Ons on an M1 Mac for AC26, but I had a similar issue. My fix was to change the relevant line in CMakeLists.txt from "python" to "python3" (it's line 149 in the example add-ons). Alternatively you could make the command "python" available by other means e.g. a symlink. Let me know in case that you need more information. You can always check in your terminal if the commands "python" or "python3" are available.
As for the AC26 python palette. I also have a developer license and I'm able to use the python palette also in AC26. I recently renewed my developer license and it took a few weeks after that for GS to upgrade it to AC26. Does the license manager say, that you have a AC26 license?
Bernd Schwarzenbacher - Archicad Add-On Developer (Downloads available on my website bschwb.com)