Found it......:) select/highlight track or tracks right click select Net Choose "unfix track segments" Then do the same again but select "unroute nets" or "uroute track paths"
I'm facing the same problem since updating to v21.x.x ! the solution described above is not a real solution as you should go to properties and uncheck the "fixed for router" box first, the go again to Net>Unroute Track Path and... may'be it will work! but you must do this for each one track segment!!! It will take you zillion years to end the unrouting of some tracks in a HD board! To me it seems that someone has "killed" an EXCELLENT feature of the EPC... probably by trying to follow the way another "flying" CAD uses, that locks any track after doing it and to unroute it you should do a 100's click job first! I'm a bit frustrated about the current version... of EPC... and its issues, or "new features" ... as I can't do my job as I had for more than 20 years... with it!