There are plenty of guides on how to install VLC on Ubuntu, but rather few on how to do it on Ubuntu 21.04. If you believe what they say then you only need to install the vlc and ubuntu-restricted-extras packages. The first package is the VLC application itself and the ubuntu-restricted-extras is supposed to contain all the needed codecs to play encrypted dvds. Except it doesn't work. You also need libdvd-pkg. Install that and all will be fine.