I can help you

I installed PB on Linux Ubuntu 19 today after many years without PB...
I fixed all my issues with the cosmic repository like this :
Code:
sudo vim /etc/apt/sources.list.d/cosmic.list
copy / past
Code:
## Note, this file is written by cloud-init on first boot of an instance
## modifications made here will not survive a re-bundle.
## if you wish to make changes you can:
## a.) add 'apt_preserve_sources_list: true' to /etc/cloud/cloud.cfg
## or do the same in user-data
## b.) add sources in /etc/apt/sources.list.d
## c.) make changes to template file /etc/cloud/templates/sources.list.tmpl
# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://archive.ubuntu.com/ubuntu cosmic main restricted
deb-src http://archive.ubuntu.com/ubuntu cosmic main restricted
## Major bug fix updates produced after the final release of the
## distribution.
deb http://archive.ubuntu.com/ubuntu cosmic-updates main restricted
deb-src http://archive.ubuntu.com/ubuntu cosmic-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://archive.ubuntu.com/ubuntu cosmic universe
deb-src http://archive.ubuntu.com/ubuntu cosmic universe
deb http://archive.ubuntu.com/ubuntu cosmic-updates universe
deb-src http://archive.ubuntu.com/ubuntu cosmic-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://archive.ubuntu.com/ubuntu cosmic multiverse
deb-src http://archive.ubuntu.com/ubuntu cosmic multiverse
deb http://archive.ubuntu.com/ubuntu cosmic-updates multiverse
deb-src http://archive.ubuntu.com/ubuntu cosmic-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://archive.ubuntu.com/ubuntu cosmic-backports main restricted universe multiverse
deb-src http://archive.ubuntu.com/ubuntu cosmic-backports main restricted universe multiverse
deb http://security.ubuntu.com/ubuntu cosmic-security main restricted
deb-src http://security.ubuntu.com/ubuntu cosmic-security main restricted
deb http://security.ubuntu.com/ubuntu cosmic-security universe
deb-src http://security.ubuntu.com/ubuntu cosmic-security universe
deb http://security.ubuntu.com/ubuntu cosmic-security multiverse
deb-src http://security.ubuntu.com/ubuntu cosmic-security 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 cosmic partner
# deb-src http://archive.canonical.com/ubuntu cosmic partner
# Debug packages
deb http://ddebs.ubuntu.com cosmic main restricted universe multiverse
deb http://ddebs.ubuntu.com cosmic-updates main restricted universe multiverse
deb http://ddebs.ubuntu.com cosmic-proposed main restricted universe multiverse
# KDE Neon
# deb http://archive.neon.kde.org/user cosmic main
# deb-src http://archive.neon.kde.org/user cosmic main
# GNU R:
# deb https://cran.r-project.org/bin/linux/ubuntu cosmic/
# deb-src https://cran.r-project.org/bin/linux/ubuntu cosmic/
# VirtualBox:
# deb http://download.virtualbox.org/virtualbox/debian cosmic contrib
# MPTCP:
# deb https://packages.nntb.no/nornet-kernel/ubuntu/ cosmic main
# deb-src https://packages.nntb.no/nornet-kernel/ubuntu/ cosmic main
next :
Code:
sudo apt update
sudo apt install xxxxxxx
It's a temporary solution. You can remove the file when all is done and do one more apt update.