I made a image of a 3D render of the Utah Teapot in the Windows 95 "3D Maze" screensaver. Since it uses elements from Windows 95, is it safe to share online? Any advice on potential copyright issues?
It's not clear what elements you're referring to.
Strictly speaking, you must have copyright or authorization for all the resources you use in a game you upload to Itch, but it's not even clear to me what you want to do.
Upload a game? Share an image? Share the 3d maze screensaver application?
If your idea is to redistribute the "3d maze" application with an image created by you, we're talking about a red flag, a Microsoft application, although old, will surely have copyright (I don't think it is this, because surely an application for Windows 95 will give many problems to run on a current Windows).
In practice, I doubt that Microsoft cares about that copyright, but legally, you wouldn't have the right.
I don't know if it's time (I'm dead tired), but I can't understand exactly what you want to share
Showing a render with that texture is not a problem, it's like showing a screenshot of the screensaver.
The problem is if you're going to redistribute the texture within a game or as part of a pack, especially if you're going to sell it. Strictly speaking, it could be a problem, although in this case I highly doubt it, I don't think Microsoft or the owner of the rights to that image are looking for people to use their texture to send them a "Cease and desist".
So having a render of an object, with the texture, shouldn't be a problem.
Still, it's important to note that some images are more problematic than others, for example, using the red cross.