If I download a foreign .deb package and open it with Discover to install, it takes tens of seconds before I will can do something with it. Possibly because Discover updates its base at start. Is it really necessary each time for opening .deb packages? I update and upgrade my system regularly.
seems related to/duplicate of bug 399732
It's not. This is due to Discover updating the sources even if you are installing something from a local .deb file. Since it is running "apt update" (or an equivalent command) in the background, you can't install anything else as there is a lock on the package list and you have to wait until the process finishes. This is frustrating as there is no obvious clue of what the reason for what is an apparently odd and unjustified behaviour is.
*** Bug 408037 has been marked as a duplicate of this bug. ***