Pokémon Masters EX offers several modes, both solo and multiplayer. Here they are, based on Poképédia and our articles.

Pokémon Masters.
ModeContent
Solo ModeThe storylines, in chapters and interludes, and each Sync Pair’s Stories
Bonus AreasFor experience and upgrade items; three difficulty levels, replayable
Co-op ModeMultiplayer battles against powerful enemies, after chapter 10; each player controls one Sync Pair at a time, and the team can launch a combined Sync Move
Battle VillaAdded in February 2020: teams of up to nine Sync Pairs for a series of battles
EventsStorylines and Sync Pairs available for a limited time

The Corbis Pokémon Center, with its shop and café, serves as a meeting point on Pasio.