SOLVED: Jellyfin Version 10.9.2: Transcoding Issues with iPhone App

[ca2ju]

I'm back to give the final report. This week, my mobile data exceeded the limit, and my internet speed and data were reduced. I took advantage of this situation to run some tests. Well, since I was using Nginx on Docker to serve my server externally from the beginning, I decided to install Apache and Nginx both outside of Docker, as I had a hunch that the problem wasn't Jellyfin but Nginx. Here are the scenarios with Bell reduced internet:

Nginx (Docker): The media wouldn't even open; they kept loading and ended up with a codec error or simply stopped.
Nginx (installed normally): Same problems as scenario 1.
Apache (outside of Docker): The movies would open but kept loading. I could see some images, but I never received a codec error or anything similar. It was clear that the issue was indeed my reduced internet speed.
In conclusion, thank you for trying to help me. From now on, I will use Apache, which has proven to be more efficient in this case.
Oh, and by the way, the Nginx and Apache configurations were basic, without security headers or anything else; they were the most basic configurations.