After a couple months of Steam Deck use, I've had good experiences, but also a lot of hitting my head against the wall trying to solve problems.
1. Peggle and Bejeweled 3 work. However, the touchscreen never seems to function correctly. Every gesture seems to go in the wrong direction.
2. Arcade Paradise should work on the device. After I get to the title screen, the game freezes. No buttons or touchscreen presses do anything.
3. While Castlevania Advance Collection functions well, my save data vanishes after closing the game.
4. Some file sizes are larger than I expected. Trials of Mana (2020) is almost 11 GB on Switch. Its Steam edition is at least 20 GB. I noticed a similar issue with The Cowabunga Collection.
5. Downloading Emudeck was easy. However, the program doesn't recognize my microSD card. Afterwards, I tried to format the card through the Steam interface. I couldn't click the Format button. A few minutes later, I double checked the microSD card with my Windows computer. No problems there. The card doesn't seem to be damaged.
6. I installed Stardew Valley (Steam version) and started a new game file. It took a few minutes to install SMAPI. It wasn't tough to get all the required files for the Welcome to Mineral Town mod, and extract their contents into the Mods folder. The SMAPI program doesn't display any errors. So I'm still not sure why I can't access the modded content. I've tried uninstalling and then re-installing both Stardew and SMAPI.