Stupid me thought it was the “optimised” per-app battery setting vs “unrestricted” that would control this.
That controls Doze, which can also potentially delay notifications.
The Freezer works entirely separate and in addition to Doze. You would need to disable both.
The nice thing about Doze these days is that you can whitelist individual apps rather than turning the whole thing off. That’s what setting the battery to “not optimized”/“unrestricted” does under the hood.