I remember the browser version coming with the install package in QGIS 2.1.8 (or so??) but cannot find the install for version 3 QGIS anywhere! Am I missing something? Please let me know where I can download the browser application..
The standalone QGIS Browser has been removed with QGIS 3. You can read it in the changelog for QGIS 3.0.
Maybe vote for some kind of return of the qbrowser, see - https://github.com/qgis/QGIS/issues/34267
One solution is to try to purge the gis-ppa and rollback to the 2.x release. It's going to lose other benefits of the gis-ppa, but might recover the older qgis app (not highly recommended), i.e.
sudo apt-get install ppa-purge sudo purge-ppa ppa:ubuntugis/ppa # rolls back installed packages sudo apt autoremove sudo apt install qgis qbrowser # is back!