Sudo gdebi package.deb in newer versions of ubuntu, this is not installed by default, so you will need to install it from. These are installed via dpkg, the debian package. I have password safe installed and running ok on my 20.04 lts notebook.
Gdebi will look for all the dependencies of the.deb file, and will install them before attempting to install the.deb file. A.deb file is a package containing all the needed files for the application, plus some utility files used for installation/removal, etc. Gdebi gdebi installs a deb package and its dependencies.