Is there a way to make Polyreduce work in viewport only? or another SOP which does this?

you can press the T on the node that you want to render and you still can switch with R wherever you want to see on the viewport.

I don't get what you are saying. I selected the node and tried the T and R. Nothing happened

Press T and click on the high-res geo node to active Render flag (color purple). This node will be going to render.

And press R and click on polyreduce node to active this branch for visualization in openGL (blue flag).

Oh, ok, now I understand what you are saying. Although I still could not get it to work. I think it's because I am rendering with Redshift and it doesn't seem to know the flags. I will have to test it out in Mantra to see if that is the problem.

But pretty sure that is why I can't get it to work.

it works the same way RS recognize the flags. Here.

Oh ya, guess it does work. Now I got it. Thank you.

Very helpful