The RoKu TV can be the problem because the data first has to be up-scaled from the WG-HD...
WG flashes here with glitter to be able to play the game in 4k (~4,000 pixels). But the fact is that with the old game engine on which the game is built and cannot be changed at its core, it can only achieve a little more than 2K (~2,160 pixels/vertical).
Even with their graphics tricks, additional software and graphics boosters, they effectively cannot achieve 4K in the game - this is controlled by the players "Hardware/Software" on their device.
Since it is a smart-compatible device with ultra-resolution, it naturally "sucks" enormously on the PC's graphics card because it is "under-challenged" - and - its own graphics unit to re-scale the data again, from scrap WG to Cinema mode.
However, it can of course also be due to the graphics card drivers if they are not up to date.
It is also known that some graphics cards are not, or not particularly, compatible with wargaming games. GeForce Experience lists these "incompatible" cards, while AMD/ASUS and others require a laborious search on the manufacturer's website.
Sometimes you can also find it by searching Google for graphics cards/PC sets.
What surprises me, however, is that the effect doesn't occur if all mods are deactivated - normally a sign that one or more mods are causing this.
The search is likely to be difficult, or at least lengthy...
I still hope you enjoy the game,