Yes those are 'crimped' fittings....common method for installations (Apollo Steel crimps)
Sometimes you can get them to loosen enough to slide down PEX Tubing by 'squeezing' the crimped portion (plier jaws on top and bottom of that section that is compressed)
OR cut them off
Using a Dremel Tool with cut off wheel cut diagonally across crimp being careful not to cut thru crimp-----just score it (or a fine tooth hack saw etc)
Then twist off using pliers.
OR
Buy a 1/2" Sharkbite Shut Off Valve (Home Depot) ----Gatorbite/Lowes
and cut PEX into right at end of old valve
Snap new Sharkbite Valve in place----done
I just cut PEX and then redo cause outside of PEX usually get scored/gouged from messing with the crimp