I’m not really sure about the exact number, but I remember trying the martingale strategy in roulette once, just betting on red or black. I think I went on a losing streak of like 20+ times. After that, I did manage to get back what I lost and make some profit. But yeah, when I tried the martingale again later, it didn’t go well, my balance wasn’t enough to cover 30 losses.
The thing is that things with the martingale are like that, it is very difficult to do them and be successful in games, personally where I had always applied them was with dice, even when trading it can be applied, but it is something that is very difficult for one to be able to do and before that you have to know how much balance you should have to lose or be willing to lose, I do not advise it, especially for novice players.