tlmgr: Local TeX Live (2019) is older than remote repository (2020)

I already tried what is suggested in the answer to the question:
“I got an error when trying to install a latex package trough tlmgr on ubuntu 20.04, verify_checksum: -5 “.

When I type this command:
tlmgr --verify-repo=none install beamer
I get:

(running on Debian, switching to user mode!)

tlmgr: Local TeX Live (2019) is older than remote repository (2020).
Cross release updates are only supported with
  update-tlmgr-latest(.sh/.exe) --update
See https://tug.org/texlive/upgrade.html for details.

I went to the link above (https://tug.org/texlive/upgrade.html) and as is suggested there, in the first place, i tried a “new installation” of texlive-latex-extra but nothing changed.
So I followed the guide. At the first point it says that the parent directory should be:

/usr/local/texlive/

and that, inside texlive directory, I should find a 2019 (or 2020) directory but the only directory I have is:
texmf-local:

ale@ale-ThinkPad-L13-Yoga:~$ ls /usr/local/texlive/
texmf-local

Eventually I looked for a “texlive/2019” or “texlive/2020” directory, but there are none:

ale@ale-ThinkPad-L13-Yoga:~$ sudo find / -iwholename */texlive/2020/*
find: ‘/run/user/1000/doc’: Permission denied
find: ‘/run/user/1000/gvfs’: Permission denied
ale@ale-ThinkPad-L13-Yoga:~$ sudo find / -iwholename */texlive/2019/*
find: ‘/run/user/1000/doc’: Permission denied
find: ‘/run/user/1000/gvfs’: Permission denied

I thought again that I did a wrong installation of texlive-latex-extra but after a reinstallation of “texlive-…” the problem was still there??

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Author: alessandro