It's supposed to be easy, but limitations of tools may obscure something as simple as a circle.

Tinkercad has limitations in the amount of used faces, you can set it to 999 but you still end up with 64.

So I looked at something like this:

https://www.tinkercad.com/things/dQZj5MgORtD-smooth-circle-by-jayteeau

And a video about how to do it (see below), basically rotating copies of the faces over each other, making a much smoother surface, and making that one new object to use.

This workaround goes fine with smallish rings, but a 100x100x100mm sphere (you have to do it twice, since it is a sphere also in 90 degrees rotation) in Tinkercad hit the maximum object size, long processing times, waiting and errors, so no go there, at least I tried ;)

In the end I took [https://www.printables.com/model/165566-sphere] Igor's sphere and limited the object size with https://myminifactory.github.io/Fast-Quadric-Mesh-Simplification/

I cut up that sphere to make a ringlike rounded object I wanted. It's printing now, will show later.