Proposed solutions:
- [confidence 85] Change the %release tag to: xanmod[#]cacule
Example: 5.12.10-xanmod1cacule.0.fc34
NOTE: This might be still too long/complicated for the kmodtool
- [confidence 75] Change the %release tag to: xm[#]cacule
Example: 5.12.10-xm1cacule.0.f34
NOTE: Using xm to substitute xanmod will be proposed first to the upstream XanMod maintainer. There are also no guarantees this will work with kmodtool

Proposed solutions:
- [confidence 85] Change the %release tag to: xanmod[#]cacule
Example: 5.12.10-xanmod1cacule.0.fc34
NOTE: This might be still too long/complicated for the kmodtool
- [confidence 75] Change the %release tag to: xm[#]cacule
Example: 5.12.10-xm1cacule.0.f34
NOTE: Using xm to substitute xanmod will be proposed first to the upstream XanMod maintainer. There are also no guarantees this will work with kmodtool

Change the %release tag to: xm[#]cacule

is now being implemented in Copr build 2249574

Implemented solution successfully fixed akmods compilation on CacULE variant

ls /var/cache/akmods/VirtualBox | grep -i xm1cacule

-rw-r--r--. 2 root   root    37K Jun 11 08:18 6.1.22-1-for-5.12.10-xm1cacule.0.fc34.log
-rw-r--r--. 1 root   root   182K Jun 11 08:18 kmod-VirtualBox-5.12.10-xm1cacule.0.fc34-6.1.22-1.fc34.x86_64.rpm