dddd

It sounds like the rear derailer housing, having been heavily compressed, may have pulled thru a ferrule a bit, impeding the smooth movement of the inner wire.

Another possibility is that a single strand or two of the inner wire broke, partially unravering within the housing and similarly impeding smooth cable movement. Broken strands inside the shifter are most common and would require a bit of care to extract the cable's end.

I would start by removing the cable anchor bolt and sliding the rear-most cable housing off of the cable, then test that the shifting movements are actuating the cable through the front-most cable housing and around the bottom bracket guide.
Use care to keep the end of the wire from fraying about, this will make reassembly easier.

A new spare inner cable wire and a length of the rear-most cable housing (plus ferrules) are really good items to have around as spares.

All praise be to Allah, your cable's onset of failure occurs when the bike is in your workshop instead of out on the road.