First, you need to narrow down your scope a bit. The French Defense has a massive amount of theory and you only need to learn a small portion of that to play it competitively.
You'll most commonly face 1. e4 e6 2. d4 d5 3. Nc3. Here, there are two main choices: 3... Nf6 and 3... Bb4. From an openings database or explorer (here, for example), you can pick the one you prefer. Notice the "Notable Games" section of the interface. These games are usually thematic and will teach you a lot about a variation with careful study. The black players are also more often than not "heroes" of the given opening, and you can look through more of their games.
Starting out, I would avoid only looking at the games of modern players. This tweet by Garry Kasparov illustrates the problem with that nicely, in my opinion. You don't need cutting-edge theory to play the opening well, you need the core ideas. These were fleshed out in the games of classical masters.
There are other lines that you need to learn as well. I commonly face the Exchange French, the Advance French, and the Tarrasch French in tournaments, and sometimes other variations. You need to know a little bit about each of these. The same process should suffice.
Apart from looking at games, I learned a great deal by reading The Flexible French by Viktor Moskalenko. The expanded version is available here.