All signal systems are openning the trades on next bar with the signal/dot/arrow/crossing and so on. All systems with no exception. All EAs and all maunl systems.
Because when bar with the signal/dot/arrow/crossing closed and this signal/dot/arrow/crossing is still on the bar (previous bar) so this signal is valid.
If bar is still open and has signal/dot/arrow/crossing so this signal/dot/arrow/crossing may be disappeared.
Try to trade pricechannel with some ... GBPJPY M1 for example just to see when dots are valid and when not.
Sorry for complicated explanation.
Of course some people are trading on open bar (in the way you said). But the problem is the following: all signal/dot/arrow/crossing which you see on your chart - on previous close bar only. So, we can not even see it on the chart on the history to understand: it is good or not.
Because of that everybody is trading as open the order on next bar with the signal.