When I try to install .deb files with "Ubuntu Software", it keeps "Waiting to install" for ever.
Install .deb packages from the terminal:
$ sudo dpkg -i <path/to/deb.deb>
$ sudo apt-get install -f
The reasoning behind apt-get install -f from the man page:
Fix; attempt to correct a system with broken dependencies in place. This option, when used with install/remove, can
omit any packages to permit APT to deduce a likely solution. If packages are specified, these have to completely
correct the problem. The option is sometimes necessary when running APT for the first time; APT itself does not allow
broken package dependencies to exist on a system. It is possible that a system's dependency structure can be so
corrupt as to require manual intervention (which usually means using dpkg --remove to eliminate some of the offending
packages). Use of this option together with -m may produce an error in some situations. Configuration Item:
Credit: Mohit Rajan's comment
Just a suggestion, Not sure if it should help but, if you frequently install packages from .deb files it's advisable to use a reliable package handler like Gdebi
However, if you like to browse for apps and install them from the same place, you should stick to Ubuntu Software Center. To trash Gnome-Software and install the classic and trusted Ubuntu Software Center follow this guide.
It seems that we are all affected by https://bugs.launchpad.net/ubuntu/+source/gnome-software/+bug/1573206.
Unfortunately there is no other solution than using another package manager to install these packages.
All you need to do is log out, and then login again.
Tested and verified this workaround fixes the issue on Ubuntu 16.04.6 LTS, clean installation.