SUMMARY
When double-clicking e.g. a .deb file and Qapt, Synaptic, Muon or any other package manager application are not installed, Discover is used to install the package.

However, Discover's current behavior (as of 5.15.4) is to check for updates first when opened, regardless of the way it is run.

This delays the installation of local packages, and depending on the internet connection, number of updates or simply a slow computer, this delay can be quite considerable.
I don't know if it's necessary to update the package database for installing local packages? 

Wouldn't it be possible to disable this check for updates whenever a local package is detected, and to start the check afterwards only in the case the user clicks on Applications or the update section?

Or perhaps add a toggle for whether or not Discover checks for updates when it's run, and keep its default behavior.

STEPS TO REPRODUCE
1. Open a local package using Discover;
2. Click Install before Discover finishes checking for updates; 

OBSERVED RESULT
Discover will check for updates first, and only after being finished will it ask for the user password using a KAuth window after the user clicks Install.

EXPECTED RESULT
Discover does not check for updates first, allowing to ask for the user password using a KAuth window soon after running Discover and clicking Install.

SOFTWARE/OS VERSIONS
Operating System: Kubuntu 19.04
KDE Plasma Version: 5.15.4
KDE Frameworks Version: 5.56.0
Qt Version: 5.12.2
Kernel Version: 5.0.0-15-generic
OS Type: 64-bit