Probably a bit stiff... Pop the screwdriver back in the gap and hammer gently, if there is more than one of you, light impact around the edges at the same time will help
I would have away with some of the foam filler and skim the surface with plaster or poly filler. Sand with medium grit paper and then wallpaper over it... Just my 2 cents
I've had the same problem in several of my properties and didn't know until I'd already moved new tenants in, I always get it done for a fixed price by https://www.drain247.co.uk/ they offer fixed prices for individual domestic issues too, so I'd say if you can't be bothered for hassle use them. Alt...
If the room is prone to condensation/humidity already then the air brick is a good idea either way, I'd say give it a go and it may well sort the issue, if not it's not all bad since it sounds to be necessary for the room anyway.
