Here it's 'transfer before 2pm and we'll send it the same _working_ day!!' And that's once you've made your appointment a week out to open an account, and maybe received everything after a few weeks (if they like you that is)...
I got the impression that N26 was mainly to challenge the latter way of working. I didn't understand what their offer was even for a free account that was better than even a 'legacy' bank in the UK (and I'm not sure they even support direct debit - which would have made it useless for any super-cheap energy/phone etc deals).
In all - yes Brexit sucks, yes they may have stayed in the UK without it (although I wouldn't have expected them to introduce anything new), but I don't think they can blame any lack of success in the UK on it.