[AX88u] IPTV and Internet over single cable?

[quovadisbg]

Hello guys,
I am struggling more than a day with this task (which seems to be quite easy) and 24hrs are a lot of time for not being able to solve an issue. So here it goes...
I am using an ISP which delivers fibre optic cable to my home, which terminates at their device (can't remove it unfortunately) which is a media convertor to RJ45.
Ports 1 and 2 are dedicated for Internet (VLAN 558, confirmed from their end) and ports 3 and 4 are dedicated for IPTV (VLAN 658).
My current setup is:

1. ISP router connecting to WAN on my router - Asus AX88U (running stock firmware, not Merlin for now if needed can be flashed);
2. Port 2 on my router goes through the floor (1.5m) and terminates at a managed switch - ZyXel GS1200-8 which is the distribution point to my NAS, NVIDIA Shield, AV Receiver, PS4 Pro, STB;

All devices have internet connectivity (1Gbps, rock solid).
3) Port 4 on my ISP router connects to Port 4 on my router;
4) Port 3 on my switch connects to the STB.
Can you advise - how to configure my router and switch so I can run properly network traffic against STB box? Current scenario, illustrated is shown below on the visio diagram + current config on my router and switch. At the moment on port 3 on switch I can see TX traffic but no RX is coming to it.

Also tried with Dual WAN configuration - still no luck.

Any ideas would be greatly appreciated, I went through all possible articles across internet but nothing actually works.
Actual values and settings in pictures - here -

https://imgur.com/a/2anzJrQ

Thanks!