Kernel Module Problem

I tried to load a compiled kernel module for the st7796 controler to get the fly-tft working, this error gets thrown when loading the kernel module:

insmod /lib/modules/6.1.99-vendor-rk35xx/kernel/drivers/gpu/drm/tiny/st7796.ko
modprobe: ERROR: could not insert 'st7796': Exec format error

The only thing I can imagine is a mismatch of the kernel header files.
Are there others available then in the repo?

linux-headers-vendor-rk35xx/bookworm,now 25.2.3 arm64 [installed]
Armbian Linux vendor headers 6.1.99-vendor-rk35xx