I found a way to play this on Mac!
First of all, you need to install Homebrew so you can easily install Wineskin Winery.
If you have already installed Homebrew (if you don't remember, open the Terminal and type brew -v), skip these steps:
1. Go to your Applications folder, go to Utilities and open the Terminal.
2. Paste the code that appears at the Homebrew page and press enter.
Now, we're going to install Wineskin. You can also skip these steps if you already installed Wineskin.
3. After succesfully installing Homebrew, go to the this page, go to "How to Install" and copy the Homebrew code.
4. Paste the code into the Terminal and press enter.
5. If succesfull, Wineskin Winery will now appear in your apps.
6. Next, open Wineskin Winery. If you get a popup saying that it is from an Unidentified Developer, click Cancel, then right click and click Open, instead.
Now for actually setting up the game:
7. Open Wineskin and Install the newest engine (in this case, it should work out well with WS11WineCX21.1.0; if you already have this engine, skip this step.) by clicking the + sign next to where it says New Engine(s) available!.
8. After the engine installation, click said engine and click "Create New Blank Wrapper". Name the wrapper whatever you want to (would recommend you to name it Sonic 3D in 2D, seems like a good name tbh) and click Ok. Now the installation should begin
9. When it finishes, it should tell you to "View Wrapper in Finder", click that. Now drag the new wrapper to any place you can remember where it is (the wineskin folder is kinda hard to access).
10. Right click the wrapper and click "Show Package Contents". Then open the Wineskin app that appears in the folder.
11. Now download .zip file of Sonic 3d in 2d and open it. At this point you can also download the Saturn DLC, unzip it and do as the guide above says.
12. Returning see a menu that says "Install Software", "Set Screen Options" and "Advanced". Click Install Software and go to "Copy a Folder Inside". Then go to where you have the unzipped folder and select it.
13. After this, it can prompt you to select where the executable file is, so select Sonic3D2d 1.27.exe
14. After this, go to Advanced and click Winetricks and search "vcrun6". A part that says dll shows, open that and select both vcrun6 and vcrun6sp6. Then click Run.
15. After installing the Winetricks, click Close and it should be done. Double click (or right-click Open) the Sonic 3D in 2D.app (which is the wrapper) and it should run fine.
But what happens if I haven't installed the Saturn DLC but I've already installed the game!?
Well what you can do is right click the Sonic 3D in 2D.app and click Show Package Contents. Then open the drive_c folder and got to Program Files. Go to the S3D2d-1.27 10-10-21 folder (the date and version shouldn't matter) and do the same as listed in the Saturn DLC guide Sotaknuck posted.
It would be cool if Sotaknuck added this to the page :)