Its not about memory size its about the asymmetric sticks. It was a classic problem with OS memory management in the past. Modern OS are better at dealing with it but it is not the optimal set up.

You’re running windows game which use proton/wine that manage memory for the game and use linux for access to RAM. The asymmetry could easily cause issues you wouldn’t notice with native apps.

I’d try removing the 16gb stick and see what happens with the games you’ve been trying. It might not he the issue but the only way to know is to test it, rather than dismiss it because its not what you expected.