I don't think we should automatically add all automatic captions as subtitle tracks, but if you want everything to be listed, you could use this in your config.

ytdl-raw-options-append=write-subs=
ytdl-raw-options-append=write-auto-subs=
ytdl-raw-options-append=sub-langs=.*

I'm not suggesting we should include all of them but can't the correct auto captions be inferred from slang config? For example, slang = 'eng,en,enUS' will load the English auto caption? I'm just wondering since mpv used to load auto captions before, if this is the intended behavior from now on then I'll close the issue.

We could pass sub-langs with whatever was set in slang, unless explicitly set otherwise.
Personally I don't really care either way.