tlmgr "unexpected return value from verify_checksum: -5"

I have a very similar problem as discussed in the post TEX564734. I am on ubuntu 20.04 and the installation via sudo apt install texlive installed a debian version in the folder /usr/share/texlive. The installed version is texlive 2019 (issuing pdflatex I get Version 3.14159265-2.6-1.40.20 (TeX Live 2019/Debian).

I then executed:

tlmgr init-usertree

however when I then try to install a new packages I get:

unexpected return value from verify_checksum: -5

In a different post, TEX537810, I saw that a solution is to update tlmgr but that does not work either.

kpsewhich --var-value=SELFAUTOPARENT

returns / which does not seem right. Indeed when I tried sudo env PATH="$PATH" ./update-tlmgr-latest.sh i get an error ./runme.sh: Cannot find TeX Live root using kpsewhich --var-value=SELFAUTOPARENT.. I added to the PATH the director /usr/share/texlive. Maybe that’s not sufficient given the Debian version? This director is the first in the PATH.

tlmgr repository list provides two repos http://contrib.texlive.info/current (tlcontrib) and http://mirror.ctan.org/systems/texlive/tlnet (main)

tlmgr key list reports a key that does not seem to have any expiration date rsa2048 2016-03-19 [E] plus another one I added from the repo maintained by Norbert Preining (tlcontrib) that has expiration date 2021-03-01.

At this point I am not sure what do to next to be able to install packages.