PNG is the safe, universal, keep-everything choice. If a WebP needs to go into an older program, a print shop, or a workflow that only speaks classic formats, PNG is usually the least surprising destination. Transparency carries over, and no detail is thrown away.
The flip side is size: PNG never discards anything, so photos come out larger than the WebP you started with. That’s the honest trade. If you need small and universal, convert to JPG instead.