thanks for your replies.
I translated the captions into english.
Regardless of one's actual choice, I think it's always interesting discussing about these subjects which are quite rare but very helpful.
Let me illustrate what I mean for the member who was asking

Let's imagine a scenario where BTC drops from $ 62k to $30K: as you can read in the sheet it's a 52% price drop. If you have 0,1 BTC, before the drop they are worth: 0,1 * $62000= $6200.
When the price drops to 30k they will be worth just $3000. In order to keep their initial value you must necesserely increase your amount of btc during a phase of price reduction.
In particular, if the price drops to 30K, in order to maintain your initial (or maximum) value of $6200 you need to increase your total btc amount to
at least 0,2067 BTC. In fact 0,2067 * $30000 = $6200.
Now, in order to open a short position for 0,2067 at $62000 you need to have an exposition of approx. $
12800, which is
double the value of your actual position.
It means that you need to open a short position for double your entire btc amount.
And this is easier said than done, especially from an emotional standpoint. And all this
just to maintain your value, not even increase it ..
This is the reason why in the end I preferred transferring my btc from Bitmex to Binance, where I sold 3/4 of them for fiat money (€).
This way, no matter how deep bitcoin drops, a certain amount of value of money will always be safe.
And that's it.
But this also means that bitmex, while it's more transparent (more on this in another topic), it must be rejected because it proves itself quite limitating compared to binance .. at least for me
For those who ask why not holding, I am basically not a holder.