As the title says. Otherwise, every rig control works perfectly, checked the automated weights and they should be fine as well, but the arm rig controls don't seem to work.
Here is a demonstration video.
How could I fix it? I tried everything that I knew. I already asked about it on Reddit, and there, someone suggested that I should change the name of the vertex groups of the arm rigs according to the name of the bones. I did it without success. I tried to regenerate the rig, but the same problem seems to persist, and I'm quite helpless and agitated by now... I don't even understand why Rigify changed the names of the vertex groups... (If that's the problem at all.) All I did was remove the leg and foot bones of the metarig (since it's a mermaid model) then I extruded the last spine bone along the tail and set its rig type to "spines.basic_tail" in the bone properties tab because I previously had problems with the tail rig where it was treated as a single large bone instead of separate bones, but the funny thing is that before I solved the tail problem there was nothing wrong with the arms, and now they don't work.