This is all very infuriating.
Not only do I have to install yet another service (postgres) just for Mattermost when every other vendor supports either MySQL or both. I have to wade through the migration process, which sic! “facilitates a smooth transition”. But there are also changes in the new postgres schema that make the migration another step more difficult.
And on top of that, OP gets an “I believe so” in response to his answer
Get your stuff together …