Back to the Steam Deck for now, testing Cyberpunk 2077 (using the Steam Deck quality preset). Can confirm the EXACT same performance hit of 5% (producing an average 42FPS during the benchmark) when switching on Game Recording. Which is an impressive result!
(Next up, I'll bounce back to the gaming laptop for Shadow of the Tomb Raider -- but this time running it at the same resolution and quality settings from the Steam Deck runs.)