I installed TeX Live following the guide on their website using the install-tl script two times. Before the second install I followed the pre-install instructions on that same website, and before any installation I removed the 2017 version that had been installed through Debian repositories.
I need a version of TeX Live >2019. I assumed the install script would install the newest version, but apparently that's not the case, since:
$ tlmgr --version
tlmgr revision 49885 (2019-01-31 20:27:00 +0100)
tlmgr using installation: /usr/share/texlive
TeX Live (http://tug.org/texlive) version 2018
However, my TeX Live installation is in ./usr/local/texlive/2021. There is no other directory with a year name in ./usr/local/texlive/.
I'm really running out of ideas, but I do need a newer version of TeX Live. I'm on Debian 10.
I followed samcarter_is_at_topanswers.xyz advice, but had to find the correct directory for my tlmgr executable. I found that through
$ sudo find -iname 'tlmgr'
.. invoked at the root directory. Running
$ /usr/local/texlive/2021/bin/x86_64-darwinlegacy/tlmgr --version
returned the newest version. However, that path was already set as described on the TeX Live page. For it to work, I deleted more directories that had been included in the 2018 installation version of TeX Live. I found those through
$ sudo find -iname '*texlive*'
invoked at the root directory. Then
$ tlmgr --version
returned the correct version.
Also, don't install TeX Live in /usr/local. Install it in your home directory.