itch.io

You can also run it on Linux using Proton.

1. Run Steam.
2. Click Add a Game then Add a Non-Steam Game.
3. Click Browse and select Sonic3D2d x.xx.exe in whatever the directory you extracted and then click Add Selected Programs.
   
4. Right-click the added game and select Properties.
5. Go to Compatibility and tick Force the use of a specific Steam Play compatibility tool, make sure Proton Experimental is selected.

Optional #1: You can make it a bit fancy by right-clicking, selecting Properties, and then change the icon to Sonic 3D Blast one and the name after the icon to Sonic 3D in 2D.

Optional #2 (non-Steam Deck users only): You can make an shortcut in the desktop by right-clicking and selecting Manage > Add desktop shortcut for quicker access.

It also works on Steam Deck, but first, you need to switch to desktop mode by either, pressing the Steam button and selecting Power, or holding the power button for a few seconds, and then select Switch to Desktop.

Open the terminal and typesudo steamos-readonly disable to enable write access on the disk, follow the above steps, use sudo steamos-readonly enable to disable them, and then switch back to gaming mode by launching Return to Gaming Mode shortcut.

Now you can play the game on your shiny OLED Steam Deck.

Alright, yeah that's naw, that's a pretty good job!