I’m the original poster. There’s been a few Revolut app updates since my original post. I thought I’d retry adding N26 as a top up, maybe something got fixed. Well, yes indeed it is now accepted. I’m able to add my N26 debit card as a top up.
Using N26 Black as a top up, I’m able to top up EUR-GBP (using N26 to convert) at a near zero rate markup. Very impressive! Can anyone confirm if N26 basic card also gives a near zero rate markup?