I didn't fix it. I don't know why it didn't work, but I was feeling a little alienated after all those tries. I then watched a video on YouTube which was much more simpler than with electrumx's tutorial. Thus, I discovered electrum personal server which seems a great implementation under some serious development.

So, I just switched to EPS. I didn't fix electrumx. I may formulated it wrongly, but "fixed" goes to my main purpose, which is running electrum without trusting anyone. I achieved it, thank you for your help.