I plan to use for positioning and tracking of areas worked for underwater mining.
I am trying to draw rings using Rectangles Ovals Digitizing plugin.
But there is very little info available.
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Besides the solution with "Geometry Generator" which intended to provide a visual solution, nevertheless, it is possible to achieve rings as completely new polygon layer using "Geometry by expression" geoalgorithm from the QGIS's Toolbox.
Pasting this expression
difference(make_circle($geometry, 100), make_circle($geometry, 50)) into 'Geometry expression' will lead to achieving the desired result, see image below.
Possible by means of the "Multi-ring buffer (constant distance)" geoalgorithm from the QGIS's Toolbox.
Afterwards, choose the required rings, others can be easily deleted.