The secret is a tiny bolt (a 3 or 2.5 mm Allen screw) very well hidden in the inner collar of the grip underneath. You must locate that small screw and loosen it dramatically. Then, the grip could be also additionally secured by a big screw inside the outer end of the bar. Please remove that screw as well. Then you have to vigorously twist the grip both ways while pulling the grip outside to "unstick" it from the handlebar metal.
The hidden inner collar screw is vital.
Now, the right hand side grip is very short to accommodate the Enviolo twist shifter. If you try to replace that grip with a new standard grip then you would need to dramatically trim that new grip. Do you really want to do it?