I need to shrink an STL file below the 25 MB threshold, so I can open it in TinkerCad. I don't care about quality, I just need it shrunk.
How can I do this?
If you have 3D software like Blender you can import your model and use the decimate modifier to lower the number of vertices and then re-export.
Here is a link to how you can do this: Simplify Geometry with the Decimate Modifier in Blender 2.9.