Is there an explanation as to what the DLCs add with the Talisman Digital Edition?
If you're looking for the rules applicable to all the various mechanics added by a given expansion, your best bet is to start reading the manual provided by nomad games. There are sections detailing the mechanics added by each expansion and their rules. This will also include the three released Digital Edition Exclusive expansions, which are not part of the Season Pass. (The Season Pass specifically only includes the physical expansions, the full Runestone card set, and a sizable bunch of extra characters with the notable [and then-controversial] exception of the Shaman character).

If you're looking to see what cards specifically are added by an expansion, you can go to My Collection from the Digital Edition's main menu, select the expansion (or even the base game), then Browse Pack. This will allow you to view all the cards from that expansion, including alternate endings and special cards like The Reaper and The Werewolf.

You can also try looking up information about the physical editions of the expansions themselves, but keep in mind that the following expansions do NOT have a physical version and only exist for the Digital Edition:


Realm of Souls Expansion (Players become ghosts when killed and interact on a separate plane until they revive or their ghosts gets killed off.)
Ancient Beasts Expansion (Adds Ancient beasts, some of which can "Apex" triggering an automatic game loss for everyone)
Clockwork Kingdom Expansion (introduces material cards and the ability to create inventions)