update

safari updates are done within macOS updates / upgrades. you either need to fully update Catalina or upgrade to Big Sur or monterey to update safari. if Catalina is up to date and you cannot upgrade to Big Sur or monterey, (not supported) then you will not be able to update safari.

EDIT: until or unless a Catalina update becomes available.

If you need to update the safari browser kindly update the macOS, for more info refer to this apple blog Update to the latest version of Safari - Apple Support.