Basically, the ROPs are in charge of the final stage of rendering a frame.

They are discrete, physical components of the GPU.

GPUs at this point are quite complex boards of many specialized kinds of processors passing information to and from each other.

Tensor cores, RT cores, CUDA cores, ROPs, etc... these are all specialized processors, specializing in different kinds of computations.

ROPs, Raster Output Processors, do varying kinds of postprocessing on the almost final stage of a rendered frame, assemble the data from other parts of the GPU and then push the finalized, rastered pixels to the frame buffer.

A rough analogy would that ROPs are in charge of the final editing pass on a paper or article before it's published, with the analagous 'research', 'fact verifying', and 'rough draft' having already been done by other parts of the GPU first.

Maybe another analogy would be that ROPs are the 'final assembly' of a frame, if constructing a frame was like building a car or aircraft.

A simpler, more literal explanation is that the ROPs perform the final stage of rendering a frame before the GPU actually pushes it out for you to see.

So... if the GPU is missing 8 ROPs... the GPU is basically bottlenecking itself, internally.