I don’t use or particularly believe in secure boot.

I have a fully encrypted root partition, with automatic unlocking using the TPM. Wasn’t even that hard to setup either. Bazzite makes it fairly easy to enroll a secure boot key if you really want that, as do some other distros. Nothing you are describing is that difficult.

A lot of systems use AppArmour instead of SELinux, as this is easier to work with while still providing enhanced security.