Forum Discussion
MasonG622 The base game is free, and they'd need to own it in the EA App in order to install it. The Steam copy wouldn't even install in macOS, and there wouldn't be any point in running Steam while they played or otherwise trying to involve it.
Additionally, the EA App may recognize the ownership of the content in Steam and not let this person claim the base game or buy any already-owned packs. The workarounds for this are to unlink the Steam and EA accounts (they can be re-linked later), or to create a new EA account.
Saves and other user files are transferrable between different types of installs, and between Windows and macOS, but this has to be done manually—EA doesn't support cloud saving for Sims 4. All user content is in Documents > Electronic Arts > The Sims 4 in both OSs.
Finally, if this isn't urgent, I would suggest waiting for the next EA sale to rebuy the content. The previous sale only ended a few days ago, so it might be a month or two until the next one, but expansions are typically 50% off or more, so it may be worth the wait.