I'm building a desktop with the new rtx 3000 series and would like to know what cpu would be good for woff.

I have an i7-9700, not overclocked, with an RTX 2070 GPU and am very happy so far. It's a new rig, but I like what I'm seeing.

I believe that WOFF only runs on a single core, so the faster the clock speed of the CPU the better. I am in the process of upgrading and have an i5-10600 on order. Chose it based on the clock speed (4.1 GHz stock, 5.0 GHz overclock potential) plus recent Tom's Hardware article that said it is a top contender for 'gaming champ' of CPU's. I am no expert so hopefully others will chime in with recommendations.

Same as 77_Scout, I have an I5 10600 here works very well, decent starting clock 4.1Ghz, enable the built-in gaming mode on the MSI board switches to 4.5 Ghz and was fairly easy to overclock more with decent cooling.
My GPU is Nvidia though.