Sorry for not replying earlier. Unfortunately, at that time I didn’t have enough time to investigate the issue further. From what I observed back then, the problem didn’t seem to be the codec itself, but rather the combination with container format, specifically MKV.
I found a set of browser test files at the time, and after running some tests I came to these conclusions. That’s where I left the topic, and in the meantime I changed my computer and reinstalled the operating system.
Today, out of curiosity, I played the video in Jellyfin and it turned out to work 🙂 It’s possible that the issue was actually on my side.
Thanks for the replies.