What will my profit be if I invested $100, if a strategy manager's all time profit increases from 200% to 300% in one day?

If you invested your $100 on this Manager from day 1, and the Manager’s overall profit was at 200% then your initial investment would have grown to $300.

If your Manager’s overall profit grew from yesterday’s 200% to today’s 300%, then your initial investment will now have grown to $400.

The % change on that day for a new investor is: (400-300)/300= 33.33%.

So, a new investor who also invested $100 and started following the Manager while his overall profit was at 200%, will also have a 33.33% ($33.33) gain on his investment making his current investment $133.33.

Your balance may be less when you start following a Strategy Manager who has open trades because of the spread being applied.