Glad to hear that worked! I’ve now included those steps in OP.
On the high postgres CPU load on startup, it sounds like you’ve been experiencing the same issue even before the PG version update. If so, that’s unrelated to the update. (Regardless, it’s recommended to run a vacuum after a PG version update. See the post-update tasks.)
Poor database/query performance could be caused by a myriad of issues. It could be corrupt indexes in the database, an under-provisioned host, a bug in Discourse which introduced a problematic query etc. It might help to open a Support topic for that.