Mostly on the administrative side. MySQL doesn’t have VACUUM to deal with, and that inevitably catches people by surprise in Postgres if they aren’t already experienced with it.

Postgres is far more flexible and capable, but it requires a lot of care and feeding, as well as deeply reading its docs to get the most out of it. MySQL is good enough for 99.99% of tech companies, and requires little to no maintenance in comparison.

Both will require you to know how to design a performant schema and query, however.