Ubuntu end of life: will snap applications still receive updates?

Snap packages are sandboxed and isolated from the apt package management system. Snap packages are permitted to have other snap packages as dependencies. Their dependencies, libraries and runtime environments are installed when the snap package is installed. This isolation ensures that snap packages can be updated independently of the base system without affecting other system components.

Therefore you can update them freely with sudo snap refresh, even if your Ubuntu distribution is end of life for apt packages. Alternatively you can upgrade an individual snap package like snapd with a command of the form sudo snap refresh snapd. You should keep the snapd package up to date because all of the other snap packages depend on it.