Thanks to several very helpful comments, I will answer my main question:
How do you update TexLive after next year's version is released?
You can use a repository with archives of previous versions.
https://ftp.math.utah.edu/pub/tex/historic/systems/texlive/2022/tlnet-final
as the time of writing,
https://ftp.math.utah.edu/pub/tex/historic/systems/texlive/
(mentionned by @cabohah as well) contains the texlive archives for years from 1996 to now.
TUG Historic FTP site seems to work well for Europe.
(answer in comments by Ulrike Fischer) If you are willing to use the command line tools (which are called by the GUI Utility anyway).
tlmgr update --repository https://ftp.math.utah.edu/pub/tex/historic/systems/texlive/2022/tlnet-final --list
gives the list of packages to update and
tlmgr update --repository https://ftp.math.utah.edu/pub/tex/historic/systems/texlive/2022/tlnet-final --all
tries to update everything. This to run with admin rights. For more flexibility consult the manual for tlmgr. Worked well on one of my computers.
(tested by me for this question on 2022, on one computer) you can insert this repository address directly as the current repository in TexLive Utility. First you will need to acknowledge a dialog that the version has changed on your usual repository and that there is no update available. You insert the archive address, then validate. This will allow to make a last update of everything you want on your installation.
Of course, you can use CTAN to install specific pieces of the texlive galaxy with bugfixes or new features. As @rallg points out, as texlive2022 is frozen, you might as well install it in the main tree so that you avoid interaction if you finally install 2023. I had no specific style or package to upgrade to this time, so I did not use that.
Other helpful questions in stackexchange:
How do I update my TeX distribution
Can I install an ancient TexLive distribution ?
the TexLive release cycle
tlmgr update --repository https://ftp.math.utah.edu/pub/tex/historic/systems/texlive/2022/tlnet-final --listto list the last 2022 updates (and--allto install them). And if you have a feature request to texlive I suggest that you write to the texlive list. When making a request do not forget that this all managed by people in their free time and that you don't pay for the software. – Ulrike Fischer Apr 15 '23 at 15:07ctan.orgweb site. In your case, with older binaries, I would cheat the system and install the package directly intotexmf-distrather than \texmf-local. That way, when you later upgrade, you will not have thetexmf-local` files over-ruling the new stuff. – rallg Apr 15 '23 at 18:00.bashrcfile (Linux) so that things are located where I want them to be located, no matter what TeX scripts say. – rallg Apr 23 '23 at 17:48tlmgrto update at all. But the comments on this answer address the updating packages issue somewhat. – Alan Munn Apr 23 '23 at 20:54.bashrc. – rallg Apr 24 '23 at 01:01