A Tower Supervisor reported they told the Local Controller to stop a departing aircraft at 2000 ft. to avoid a traffic confliction resulting in the departure flying below the Minimum Vectoring Altitude.

Narrative

Here is a copy of the MOR I filed. Aircraft X; IFR; departed ZZZ Runway XXL. Aircraft Y VFR was in the departure corridor on a point out at 2500 ft. Based on the position of Aircraft X and Aircraft Y; Aircraft X was issued to maintain 2000 ft. After passing Aircraft Y the Aircraft X was re-issued a climb to 4000 ft; then shipped to Departure. The Tower had Aircraft X and Aircraft Y in sight at all time and the closest vertical distance was 500 ft. I was working GC and OS position. When the Local Control (LC) who had a point out in the departure corridor rolled an Aircraft X off of Runway XXL at ZZZ. I figured they had a plan. It turn out they did not. All the Controller said was that the Aircraft Y turned different this time verses the other time on the arc. It did not seem to me that the flight check was flying any different than the last arc. As the Supervisor I thought I would offer the LC Controller assistance on a way out of this VFR point out in the departure corridor. I turned and looked at the LC and said; '90? heading'. This suggestion was done in a timely enough manner to have avoided the Aircraft Y. The Controller did not take that advice and had the Aircraft X continue on a 140 or 180 heading. At this this point the situation with the Aircraft X (IFR) and Aircraft Y (VFR) was imminent. If the LC Controller had turned the Aircraft X (IFR) East it would have been towards the Aircraft Y. If the LC had turned them West there was a higher MVA and Aircraft Y was moving in that direction and it still would have been an issue. I concluded that the best course of action was to use altitude. I said something along the lines of; 'stop them at 2000'. This advice the LC Controller took. This gave us 500 ft. between the Aircraft Y and the Aircraft X. After they had passed the LC Controller climbed the Aircraft X back to 4000 ft. and switched them to Departure. LC had Aircraft Y and Aircraft X in sight and was talking with Aircraft X. Also the there is a 3000 ft. MVA in that area however all the tall building and antennas are well west of the heading Aircraft X was on. This is more than likely a MVA bust; but it could have been worse if allowed to progress. Next time I will have LC; cancel the take-off and hold and wait for Aircraft Y to clear the departure corridor. Or next time instead of making the 090 heading a suggestion; I as the Supervisor will make it mandatory compliance turn. Please note; I have been told on many occasions that I am too quick to interfere with controllers plans and that I need to not intervene as much and I need to work from personal power and not positional power. I have been told this many times. I could see that this was going to be a problem when LC rolled Aircraft X that was why I helped them with the 090 heading suggestion when the Aircraft X was at mid field; at a safe alt and safe attitude. I realize that 2000 ft. was below the MVA but in my opinion by the time I said stop them at 2; there were no other good options left. I would rather have a MVA issue than a crash.