Someone got into my Steam account and added cross save accounts for Microsoft, Epic and Playstation which were not mine.
I have fixed the Steam breach and all is safe with my Steam account now.
I have bought all of the expansions which state they all only have licenses for the steam platform.
Can this other player play my purchased expansions through the cross save accounts that are not steam?
Hey there, expansion DLC is locked to the platform it was bought on, so no, DLC bought on Steam is not accessible when playing the cross-saved characters on another platform unless the platform account holder buys it there.
Dungeon keys and reward passes count as in-game purchases, those will be available on any of the linked platform, not just the ones they were purchased on.