As I am using Degiro, I have no access to cryptocurrencies. However, when looking for "Bitcoin", I found this action: Bitcoin Group SE
It looks like the chart of this action is following the bitcoin one. So what is it exactly?
Thank you for your help
Bitcoin Group SE is a German venture capital company so this is shares of a company that happens to be have "Bitcoin" in the name and so is not a crytpocurrency at all. According to the English language section of their website (https://www.bitcoingroup.com/en/) they are deeply invested in banks that deal in Bitcoin (at least that's how I read their financial data). This may explain their relatively high correlation to the price of Bitcoin.
Please note that companies don't have to have a name that has anything to do with what they do - Brooks MacDonald Group, for example, don't have much to do with fast food (https://www.londonstockexchange.com/stock/BRK/brooks-macdonald-group-plc/company-page?lang=en). Make sure you read everything about an instrument before investing as it may not always be exactly what you think you are investing in.
Most of what you needed to know was on the page that you linked as it is listed as an equity instrument but Bloomberg filled in the gaps for me: https://www.bloomberg.com/profile/company/ADE:GR
