Screen grabs

Hi guys...Sometimes I shoot videos with my Canon R6 Mark 1 at 4k/29fps (I'm mostly a Stills photographer.) When I take a screen grab in PP and import the jpg into LR, the image isn't bad. However, I'd like them to be sharper.

If I was to start filming with the Canon R5 C at 8k, would the resulting screen grab be sharper?

Thanks

John