If you don't mind cracking it open, I'd recommend picking up a bigger SSD. I swapped my 64 GB for a 1TB and it's been night and day.
Also, look into something like Deckmate. You can buy it from them or get the 3D files for a donation and it allows you to mount things to the Steam Deck. Their kickstand even doubles as an 2x microSD card holder.
Have you tried Vampire Survivors or Brotato?