Re: Sims3pack files won't open and install through my launcher on my 2018 Macbook?

@novacanova  The issue is probably that the OS doesn't "know" what app to use to open the Sims3Packs.  But it's easy enough to get around that.  Put one pack in Documents\Electronic Arts\The Sims 3\Downloads, open the launcher, and see whether it shows up in the Downloads tab.  If it does, install it, move some more packs over, install those, etc.

It's also a good idea to remove the packs from the Downloads folder once you've installed them, as the launcher can get bogged down trying to read too many files.  You can always set aside the downloads for later use, just make sure they're elsewhere.