I think this already happens. If you reduce the quality the textures they become lower resolution. And in phones I think due to the compression algorithms for the stores they aren’t as high quality as the pc version even on max Graphical settings.
However this is long time ago so I am not 100% sure about this.
Im pretty sure that on mobile Roblox dynamically adjusts the resolution of the textures based on the available memory, although sometimes it feels buggy. I hope Roblox adds this feature into the official settings where you can change the modes between Low, Medium, and High(maybe ultra?) for 512 - 1024, 1024 - 2048, 2048 - 8192.
I wish but we don’t even have the ability to change the render resolution.
Like my screen is 4K and Roblox render resolution runs at 4K wasting a lot more resources than needed, so without even having a basic thing such as that I doubt they will give us the option to change more game specific settings.