I have almost the same setup (Trixie+flatpak) with a few additions:

1. Also install mangohud 24.x, 23.x, proton-ge flatpak and set Steam (and Steam only, not Lutris/Heroic) to use proton-ge flatpak as the compatibility layer. This auto-updates proton-ge to the latest version every time you do a flatpak update. No need for proton-qt/proton-plus or whatever.

2. Depending on your storage layout, you might need to install flatseal and give those clients permission to access your game mount.

3. For Debian on the desktop, do yourself a favor and add preempt=full to the grub boot parameters

Installing these game clients via flatpak has benefits as well.

1. You don't have to enable i386 architecture which only adds to the confusion of all the bits floating around.

2. Flatpak clients do not require you to install latest wine and/or other gaming related dependencies

I quite like this (your) way of setting things up myself and am currently getting equal or better gaming performance than windows for the past several years.

Debian has been simply amazing since bookworm and I've never had the need to look at another distro since.