The MangoHUD version shown in the performance overlay clearly is different in the screenshot (Gundam LCD is v0.6.9-1-22-g1d8f9f6 and OLED is v0.7.0-54g9393066). So possibly one is on 3.5 and one on 3.5.1 which is not as bad as 3.4 vs 3.5, but still not properly matched.
If your computer runs Windows, you need to install an ext4 filesystem driver to be able to read and write to the card after it was formatted in the Steam Deck.