Sometimes, a deb package may not be installed on Ubuntu or Debian because it depends on other packages to run, or it may not be compatible with the system version you are running on.
Fortunately, you can force install deb packages via the terminal using simple commands, but it's not highly recommended because it may render your system unstable or useless and you will end up reinstalling your operating system, so use these commands at your own risk! You can also use QApt Package Installer for Ubuntu, which is a package manager that allows to view and install deb packages by resolving and downloading dependencies, which I think a safe option.
To force install a deb package from the terminal, use one of these commands:
sudo dpkg -i --force-depends package.deb
sudo dpkg -i --force-all package.deb
Replace "package.deb" with the name of the Debian package you want to force install. For QApt Package Installer, you can install it under Ubuntu with this command:
sudo apt-get install qapt-deb-installer