I’m not sure I properly understand your problem, but perhabs your kernel is compiled with CONFIG_MODULE_SIG_FORCE. You can check with grep CONFIG_MODULE_SIG_FORCE /boot/config-$(uname -r). If it isn’t you could try and run the kernel with module.sig_enforce=0 as a parameter and see if that helps.
If you don’t need secure boot, then just disable it (if possible).