Make mpv hold on the last picture instead of closing

User MelBurslan answered in a comment under this more general question (Is it possible to specify a path in which one of the directory levels is variable?):

as long as the varying directory level is a single directory, what I mean by that, if you have /dir1/dirX/dir3/dir4 and the dirX part is not changing like dirX/dirY/dirZ but can only be one of the dirX, dirY or dirZ, then you can reference /dir1/dirX/dir3/dir4 as /dir1/*/dir3/dir4

So, in the case above, the command that works is simply something like mpv /media/username/*/VIDEO_TS

As seen in man mpv:

   --sub-auto=<no|exact|fuzzy|all>, --no-sub-auto
          Load additional subtitle files matching the video filename. The
          parameter specifies how external subtitle files are matched.
          exact is enabled by default.

          no     Don't automatically load external subtitle files.

          exact  Load the media filename with subtitle file extension
                 (default).

          fuzzy  Load all subs containing media filename.

          all    Load all subs in the current and --sub-paths directories.

exact would seem like the appropriate choice, but since it's the default and it doesn't load files like [video name minus extension].srt, fuzzy is the next best bet and it works on my system.

So just echo "sub-auto=fuzzy" >> ~/.config/mpv/mpv.conf.