I haven't completely understood what you have done, but in respect to your own answer it is in general possible to run 32 bit programs on a RasPi running a 32 bit or a 64 bit kernel. You cannot run a 64 bit program on a 32 bit kernel, which is default. For this you must use a 64 bit kernel. Raspbian Buster has a precompiled 64 bit kernel available together ...
By creating that post, I noticed that aarch64 is the crucial part.
I need aarch64-linux-gnu-g++ for compilation and the resulting image will run directly.
It seems that - unlike Windows - 32bit programs cannot be run on a 64bit architecture.
Watchdog is built into the Raspbian kernel using CONFIG_WATCHDOG=y in kernel parameters, so rmmod is not possible unless you rebuild the kernel.
/proc/sys/kernel/watchdog is not implemented in Raspbian either. I'm not sure about Arch, but judging by your question the situation there is similar.
You don't need GRUB to pass parameters to the kernel: on ...