Both solutions seen in the OP picture, solder mesh on trace and Silkscreen cover, are cheap and weak solutions for technical problems. Often seen in cheap powersupplies, to save money. And sometimes implementation is even done wrong.
Solder mesh:
Weak workaround for using thicker copper core/plating. For wave soldering, you cannot remove the SR completely, as this will give undefined solder thickness & some drops/tears on the trace. It will also increase risk of bending if both layers are not weighted equally. Therefore this is done as a mesh.
In the OP picture, this is even done wrong, as the mesh should follow the current flow. They mainly only have the outer surrounding shape, the inner crossings are 90° to current flow, therefore somehow ineffective.
Silkscreen cover:
Besides standard silkscreen, there are a lot of different materials with special properties available. See
https://www.dupont.com/products-and...rials/brands/screen-printed-inks-for-pcb.html
In the OP picture, it could be also normal silkscreen, covering some traces, to increase insulation resistance, if the pcb is too close to housing.
I fully agree to all of you that both solutions are not "best practice" for proper pcb design.
I'm just waiting when we will see PCBs with SCO / STH on CEM1 again :laugh: