Quote from: NeoArkan on Today at 10:18:38 PM

To clarify what I did :
-I have downloaded Electrum 4.2.1 using macOS Monterey Version 12.3.1
-I have created a new standard wallet

This doesn't answer if you downloaded your Electrum from the one and only site: https://electrum.org
To be sure that you downloaded the genuine Electrum you should verify its signature. There's a thread which describes in detail how to do that.

There's nothing wrong when you already have created a new standard wallet, but you add an extra step which also costs you transaction fee for an on-chain transaction.
Then you can only sweep the coin's private (mini)key into your wallet (the address button offers addresses which belong to your existing Electrum wallet) OR not really recommended for newbies because it's error prone, directly to a provided destination address of your choice (be careful to thoroughly check that the destination address is copied without error).

Quote from: NeoArkan on Today at 10:18:38 PM

However, if I understand well what I have to do is :
-Choose the option "Create New Wallet"
-When the dialog box asks "What kind of wallet do you want to create ? " --> I have to choose "Import bitcoin addresses or Private keys"
-Enter the private key of the "Cascasius" coin in the dialog box and click on "Next"
-After that, my Electrum wallet (the new one then) should show exactly 1.BTC as balance and I will have the possibility to send the amount on the exchange platform of my choice

Is that correct ?

Yes, that is what was described by hosseinimir93 and this procedure doesn't require an on-chain transaction with transaction fee, at least not for the step to open the funds in Electrum. To transfer the funds to an exchange would require an on-chain transaction with transaction fee. But currently the transaction fees are not high, nothing to worry about.

I would assume that an unpeeled Casascius coin, still fully funded, is a collectible which is worth more than the sole 1BTC it holds. But how to sell it safely is a whole other story and I'm no expert on this to give any advise. I personally wouldn't dare to ship such an item somewhere and face-2-face transactions pose other risks which should not be underestimated. I have no idea how Casascius coins are traded safely nowadays. Likely there are some threads in this forum for this.
Not to say that currently is maybe not the best time to sell your BTC. You missed exchange rates of more than 50k EUR/BTC more than once... (sorry, that's easy said when looking at past exchange rates).