AMD artificially blocked PCI-E 4.0 updates to many B450 motherboards - OEM rebranded B450 motherboards,ie,B550A could support it. So now basically just to add PCI-E 4.0 to the main slot and a single M2 slot, you are paying significantly more.
An X570 will allow dual PCI-E 4.0 M2 slots. You can get plenty of X570 motherboards for £150~£200 now.
I've been a little put off by all the negative talk around the chipset fans. No idea if it's really an issue at all but I'll be looking at keeping whatever board I buy for a good few years so I would be worried about something failing. The price is only a slight issue, I don't mind paying for something that will last and that will fill my very limited needs.