What settings do I use to export a high-quality *.gif file?
I created a loader animation icon using the shape tool (ellipse). But when I export my animation, the circle has jagged edges and the quality isn't good.
What are good settings to prevent these edges and have a high-quality
.gif as a result?
There's really no such thing as a high-quality gif. The format was developed in the early 1990s and is limited to 256 colours, one of which may be fully transparent.
Best you can do is optimize it for the current background colour, and choose fills & blends that do not involve a lot of intermediate shades.
If you want a basic spinner / throbber icon and your target is modern browsers you can get much better results with css animation and/or svg.