So I've just freshly installed 21.04.
I've got the layout set to Cupertino. Initially the dock disappeared but a restart seems to have ironed out that problem.
However, when opening Firefox it's not showing up in the dock. Once I minimise the window I can't get back onto the FF without minimising other windows or Alt-Tabbing. It's very odd.
Edit: Another reboot seems to have fixed this.