I’m trying to add a Bezier circle inside another Bezier flat surface in Edit Mode (an operation that worked normally in my previous project - bottom right of the image), but today Blender decided it would give me a hard time!
The circle is not circular at all
I tried adding an independent circle (at this point it looks normal), and then joining the two objects, but that too makes it look distorted…
I also tried changing the handle types, but that did nothing useful!
It looks to me like you’ve scaled the curve in object mode.
Scaling is really weird with curves. Even new objects added in edit mode AFTER you scale are affected by the scale. You can apply the scale of the original curve before adding the circle, but it’ll probably change the shape.