Do you understand how bitmaps and raster drawing works? Everything is represented as a 2d array of pixels. 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.
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.
Do you understand how bitmaps and raster drawing works? Everything is represented as a 2d array of pixels. 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.
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.