Creating polygons via snapping to circle line

I am trying to digitalize my research areas. Those do have a radius of 250m which I created via the buffer and polygons to lines functions. Now I try to create polygons with the different land uses. However, when I want to snap it to the outer 250m line, it does not use the whole circle-part to snap to, but the polygon creates straight lines to the point I clicked onto.

It used to work beforehand and I have no idea what I changed (never worked with QGIS before and reading the introduction and playing around with different things did not work out).

I use QGIS 3.16 Hannover and my settings are Snapping enabled, All Layers, Segment, 14px, topological editing enabled, Tracing enabled, avoid overlap on active layer enabled, self snapping enabled.

If you need more information I am happy to post it.