Not sure what they used stock, one guy I’ve seen on YouTube who’s called tech yes city seems to like using arctic mx4 on gpus, I don’t think it’s conductive.
Have heard things about kryonaut, their paste seems to be a pain to apply imo.
Those blue and white stuffs are thermal pads, usually with different thickness for different places on the GPU for best results possible, it seems that they used colored thermal pads to keep track of the thickness.
that blue gunk on VRMs is not termal paste, It's what's left of thermal pads. Applying termal paste won't work as the gap between heatsink and VRM is too large. What you need is a new set of termal pads of appropriate thickness. 3M makes those in all shapes and sizes. Color is irrelevant.