https://forums.whonix.org/t/using-whonix-workstation-as-a-disposablevm-dispvm made me look into this again.
Btw this was deprecated so the code could be simplified. Times of broken RecommendedTBBVersions were advertised higher version numbers were advertised so it made sense for tb-updater to automatically download the next lower one in RecommendedTBBVersions are fortunately over. Nowadays tb-updater only downloads the version which was selected and would fail and show an error message if that did not work.
The old update-torbrowser behavior was to only show alpha, beta and rc versions when the respective --alpha switches were used. That was fixed with above commit and same was done for --hardened. As of the above commit, hardened versions will only be shown in the download confirmation screen when using --hardened.
Originally this was implemented in different times (of Whonix 12, I think). Tor Browser was not installed by default by that time. It will be in Whonix 14 everywhere (including in Non-Qubes-Whonix). Back then the motivation was to hide alpha, beta and rc versions from the download confirmation screen menu to improve usability, to prevent most users from downloading alpha versions without knowing what they are doing. Also if I remember right, Tor Browser internal updater did not exist back then.
Since Whonix 13 / 14 update-torbrowser has a different recommended use. It’s called a downloader rather than updater. (update-torbrowser and tb-updater should be renamed… To what?) Tor Browser internal updater is recommended for most users. update-torbrowser is rather used to implement up to date versions of Tor Browsers in newly created AppVMs inherited from updated TemplateVMs`. Recommended to reinstall Tor Browser. And could also be recommended to change from stable to alpha and/or hardened.
For Whonix 14 update-torbrowser I am wondering if --alpha, --beta, --rc, --hardened should be removed. RecommendedTBBVersions is difficult to parse. Perhaps alpha versions ("6.5a4",) could be detected as "a character a followed by some digit without a previous - (dash). Then both, alpha and hardened versions would be shown in the download confirmation screen.