@snadge
I'm currently investigating 4k video issues over fast ethernet ports for my parents.
They are on a eci lantiq cab, they were using a Netgear dm200 in bridge mode as the modem, but as the lights are not easy to understand I swapped it to a comtrend vr3030, makes family tech support easier.
Anyway they currently have a tenda nova MW3 mesh network in place, lg 4k TV is wired into one of the nodes, but TV will never push more than hd content, FTTC syncs at 60/20.
If I install a Mikrotik wireless bridge, even something as cheap as two Mikrotik hAP lites, which are £17.99 on Amazon, 4k works on iPlayer, YouTube, Amazon Prime and Disney+.
All devices have fast ethernet ports,but the Mikrotik QoS just seems to do what is needed to deliver 4k content.
I have seen the Fritz!box 7583 is available, latest Intel lantiq chipset vrx618, not seen a good price as of yet.