Ok, so back in 2018 I owned the Fritz!Box 3490 (great little DSL router) and I asked AVM Support regarding my PLUSNET (Broadband) DSL connection (PPPoE) and being able to use PlusNet Youview (IPTV) service to watch TV.
Below is AVM supports response which maybe of help – not sure 
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I do not have specific information on Plusnet services with IPTV.
In order to use IPTV, the FRITZ!Box usually must be connected to an IPTV set-top device that establishes a second virtual connection via VLAN. It may be possible to enter this VLAN ID in the FRITZ!Box in section “Change Connection Settings” on page “Internet > Account Information”. Please consult the service provider for further information on how their service can be used with a NAT router.
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In a completely sane world, madness is the only freedom (J.G.Ballard).
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