After encountering the reported bug in 3.16 + Qt 5.9.5 (https://github.com/qgis/QGIS/issues/39693), I tried to remove and reinstall and got the broken dependencies below.
user@dell: sudo apt install qgis qgis-plugin-grass
Reading package lists... Done
Building dependency tree
Reading state information... Done
Some packages could not be installed. This may mean that you have
requested an impossible situation or if you are using the unstable
distribution that some required packages have not yet been created
or been moved out of Incoming.
The following information may help to resolve the situation:
The following packages have unmet dependencies:
qgis : Depends: libgdal20 (>= 1.8.0) but it is not going to be installed
Depends: libqgis-3d3.16.0 but it is not going to be installed
Depends: libqgis-analysis3.16.0 but it is not going to be installed
Depends: libqgis-app3.16.0 but it is not going to be installed
Depends: libqgis-core3.16.0 but it is not going to be installed
Depends: libqgis-gui3.16.0 but it is not going to be installed
Depends: python3-qgis (= 1:3.16.0+28bionic) but it is not going to be installed
Depends: qgis-providers (= 1:3.16.0+28bionic) but it is not going to be installed
qgis-plugin-grass : Depends: qgis-provider-grass (= 1:3.16.0+28bionic) but it is not going to be installed
Depends: grass740
Depends: libgdal20 (>= 1.8.0) but it is not going to be installed
Depends: libqgis-app3.16.0 but it is not going to be installed
Depends: libqgis-core3.16.0 but it is not going to be installed
Depends: libqgis-gui3.16.0 but it is not going to be installed
Depends: libqgisgrass7-3.16.0 but it is not going to be installed
E: Unable to correct problems, you have held broken packages.
System is Ubuntu 18.04. Sources are:
# deb cdrom:[Ubuntu 18.04 _Bionic_ - Build amd64 LIVE Binary 20180608-09:38]/ bionic main
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://il.archive.ubuntu.com/ubuntu/ bionic main restricted
# deb-src http://il.archive.ubuntu.com/ubuntu/ bionic main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://il.archive.ubuntu.com/ubuntu/ bionic-updates main restricted
# deb-src http://il.archive.ubuntu.com/ubuntu/ bionic-updates main restricted
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://il.archive.ubuntu.com/ubuntu/ bionic universe
# deb-src http://il.archive.ubuntu.com/ubuntu/ bionic universe
deb http://il.archive.ubuntu.com/ubuntu/ bionic-updates universe
# deb-src http://il.archive.ubuntu.com/ubuntu/ bionic-updates universe
## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team, and may not be under a free licence. Please satisfy yourself as to
## your rights to use the software. Also, please note that software in
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://il.archive.ubuntu.com/ubuntu/ bionic multiverse
# deb-src http://il.archive.ubuntu.com/ubuntu/ bionic multiverse
deb http://il.archive.ubuntu.com/ubuntu/ bionic-updates multiverse
# deb-src http://il.archive.ubuntu.com/ubuntu/ bionic-updates multiverse
## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://il.archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
# deb-src http://il.archive.ubuntu.com/ubuntu/ bionic-backports main restricted universe multiverse
## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
deb http://archive.canonical.com/ubuntu bionic partner
# deb-src http://archive.canonical.com/ubuntu bionic partner
deb http://security.ubuntu.com/ubuntu bionic-security main restricted
# deb-src http://security.ubuntu.com/ubuntu bionic-security main restricted
deb http://security.ubuntu.com/ubuntu bionic-security universe
# deb-src http://security.ubuntu.com/ubuntu bionic-security universe
deb http://security.ubuntu.com/ubuntu bionic-security multiverse
# deb-src http://security.ubuntu.com/ubuntu bionic-security multiverse
deb https://qgis.org/ubuntu bionic main
# deb-src https://qgis.org/ubuntu bionic main
deb [arch=amd64] https://download.docker.com/linux/ubuntu bionic stable
# deb-src [arch=amd64] https://download.docker.com/linux/ubuntu bionic stable
deb https://qgis.org/ubuntu-ltr bionic main
# deb-src https://qgis.org/ubuntu-ltr bionic main```
