Currently, when there are multiple media (tracklists) attached to a release, each media can have it's own distinct "Medium title".

There are vinyl records, and compact cassettes with distinct titles on what would typically be labeled "Side A" and "Side B" – which do not actually include any ordered labeling (i.e. no "1" then "2", or "A" then "B", on opposite surfaces.)

For example, Information Society's 1990 release "Hack", labels opposite side of the cassette release as "Gilligan Side" and "Skipper Side". While the vinyl LP release labels opposite surfaces as "Scooby Side" and "Shaggy Side". I think there are some Monty Python LPs that do this kind of thing too. And a bunch of non-music releases, where each side has a special purpose, and does not have a deliberate, single, ordered tracklist.

Currently, MusicBrainz merges the "A" and "B" sides of a dual sided medium together into a single track list. So, it is not possible to set a "Medium title" for each half of the single tracklist.

Compaire:

https://musicbrainz.org/release/f5daa2b1-3bb6-4dbc-8371-8aa0908856bd

https://www.discogs.com/release/184813-Information-Society-Hack

Update:

After I wrote this, I found https://tickets.metabrainz.org/browse/MBS-6680 which might be related...

And, I don't know, maybe this too https://tickets.metabrainz.org/browse/MBS-11129