snapd and SElinux
Installing and using SELinux on Ubuntu should be considered as an "advanced use-case", since Ubuntu uses AppArmor by default.
One of the consequences of using SELinux instead of AppArmor is that you loose snapd functionality, since snapd requires AppArmor, and can't use SELinux.
Also note that the SELinux packages for Ubuntu is in the "Universe" repository, which means they are maintained by the community and not Canonical.