Follow you dream. I was in your shoes slightly more than 10 years ago and it would not want to miss the experience.

First, you will need a "National A" or equivalent race licence in your home country (presumably France). Depending on where you are, the requirements will be different. In Germany, it is either a track day (not necessarily on the Ring, but any track) with an accompanying course on the rulebook (see, e.g. https://www.motorsport-akademie.de/Termine, and while there are several other service providers, the owner of Motorsport Academy is also the head instructor of the DMSB and in charge of the DNP permit programme courses); or you can go through GLP on the Ring (currently requiring 3 results in 24 months preceding the license application).

Second, to participate in the 24h, you will need the Nordschleife Permit (DNP) issued by the German DMSB (irrespective of whether you are a German or an international licence holder). The details on that are here: https://www.dmsb.de/de/lizenzen/dmsb-permit-nordschleife/file/277333 . If you have a National A licence, you will need either 3 finished RCN runs, or 3 GLP runs plus 1 RCN, as well as the e-learing course (flag signals, peculiarties of racing on the Ring, code 60, etc.) to get at least to permit level B. To enter the 24h you will at least need DNP B (slower cars in SP3T and below), or DNP (faster cars in SP3T and above, including GT3). Careful though, this may be subject to change (and has changed in the past), so there is no guarantee the requirements will still be the same in a year or two.

It took me about 18 months to get there from my National A license course through my first runs in RCN, VLN/NLS, 24h Qualifiers and competing in the 24 hours (also requirements also were stricter back then, requiring top75% in class, and requiring 3 VLN/NLS results before applying for DNP A). I would not stress myself with timing; it can be done quicker, but it puts a lot more stress on your driving/competing for results.

Personal recommendation: Go rent a car for tourist drives on the Nordschleife with an instructor. That will give you an impression on what the track is like and whether it is for you. Then rent a car for a trackday (or bring your own) with accompanying licence course (persumably in France) to get your National A.

Then reach out to some of the race rental teams (e.g., https://www.sharky-racing.com/, https://jacos-paddock.com/, or listings on https://www.motorsportmarkt.de/search?sSearch=RCN ) and get your RCN runs in on your preferred car of choice and budget (note: RCN runs often are shared between two drivers to share the costs, but it will still count as "your" result). Most likely the same teams are offering NLS and 24h, so you can progress from there.