What pace should I run in VO2Max workouts

The pace during the intensity intervals in VO2Max workouts is high.

The pace should be well-above your anaerobic threshold (pace at which maximal lactate steady state is reached).

For long HIITS I would rate them on RPE 15-16 (on scale of 20), and

for short HIITS maybe RPE 17-18.

Most important - try to go as hard as possible by achieving the highest possible average pace across the intervals without having too much variance between slowest and fastest intervals.

If your last interval is significantly slower than the previous ones than either you ran too fast at the start or the number of intervals is still too high for your current level of fitness.