Hello I do not have answers for you, I just want to say I find your illustrations delightful

I don't think anyone has mentioned this but HDMI is just Cat-6 with a fancy hat. You can run cat-6 cabling through your attic, down the walls, etc., as if you were setting up a standard Ethernet run. Then, slap some rj-45 to hdmi adapters on each, and voila! Or you could just put proper hdmi heads on the cable ends and skip the adapters.

EDIT: Amazon product link with diagrams.

https://a.co/d/02iebocu

I played borderlands 4 with exactly the setup in the post with a wifi 6 router and while the latency was noticable it wasn't enough to make borderlands unplayable.

If you measure it and it is less than 10m (the physical limit of hdmi without a repeater) then you might consider a floor cable canal. They usually come in a variety of colors, don't require adheisive or screwing and are just simple things to keep people from tripping on cables

I have one of these on a doorway, to connect a pc to a tv and it works good enough

Fiber optic hdmi cable works well over long ranges. To secure cable I just got some cheap plastic clips with adhesive, since I didn't feel like drilling holes.

Search for 'Active optical HDMI cable 20m', you'll be greatful for extra on each end and the cable is very thin cable, just never kink it. You can get up to 48Gbps 8k 60hz 12 bit color depth. This cable would be easy to hide under a rug or tack along the floor board around the walls or even ceil.

If you don't need crazy resolution and frame rates you can get wireless HDMI extenders but they can get pricey.

Could you swap the tv and seating so the tv is on the same wall as computer?

The cat 5e / cat 6 hdmi adapters are incredibly cool! If you can run above, below, or around this would be a great solution too.
(Please don’t run wiring under carpet for everyone’s safety).

*Yes, I know HDMI is low voltage, but I’d rather people takeaway the “don’t do this” vs. the nuanced risk.

If you are in US, you can buy a 48gbps 50 meter fiber hdmi for 200 bucks, and run it along the bottom of walls from pc to tv and put some masking tape on it.

https://a.co/d/0j6wplnq

Expensive, but would work nicely. There would still be question of wireless controller working since there’s a wall b/w tv & pc.

Have you considered a projector? Just saying, I’ve got one recently, and your floor plan seems ideal for that. Also, as a bonus point, you may have a much bigger screen, for fully immersive experience.

oof, 10m is the limit of what hdmi can do without degrading. you'd need a repeater.your current setup is probably better unless moving the pc to the tv is an option.