Opensource

Do you understand how bitmaps and raster drawing works?

Yes I know the difference between vector and bitmaps

Everything is represented as a 2d array of pixels.

Only after the rasterization has taken place.

The circle selection before you paint can be moved/scaled/etc and then when you actually want to draw the circle trace the path with the appropriate thickness and use antialiasing if you need to smooth it.

The problem is that the selection itself can lose information, it's handled internally as a raster mask. That's why you should use a real vector shape.

If you want to make vector drawings, take a look at InkScape. GIMP is the wrong tool for that, so use the right tool for the job if that’s what you want to do.

No. Raster editors can support vector shapes. They vectors are rasterized during the final export, not while creating the shape (which is lossy and what selection shapes are).

Look at how to create, move and transform a circle in photoshop (or if you don’t want to give adobe money, use photopea).