I've tried a bunch of times, but haven't really found anything that's been particularly useful as a steamdeck 3d printed accessory. Probably the closest I've come is a steamdeck gridfinity storage solution for my desk, and a stand to play if I felt like using an xbox controller instead of holding the deck.
Here's the ones linked from the video, nothing in there was super interesting. Best one of the bunch was the charger insert, but I've found it to be annoying to use. I just go back to a small bag to stuff the charger into.
Steam Deck Drop Protector (LupusWorax): https://www.printables.com/model/254680-steam-deck-lifesaver-drop-protection
Carrying Case Insert (Strider460): https://www.printables.com/model/202185-steam-deck-carrying-case-insert
Dock Cable Cover (yugi): https://www.printables.com/model/378549-steam-deck-dock-cable-cover
Charger Dock (Strider460): https://www.printables.com/model/230276-steam-deck-charger-dock
Steam Pal (Froggerdog): https://www.thingiverse.com/thing:5511683
Joystick Guards (MarkWithASea_240810): https://www.printables.com/model/723941-steam-deck-stick-guard-split