I'll pitch in here with my perspective as a software developer and lifelong music listener.
Back in 2023 I evaluated Emby and Jellyfin (Docker containers) on my TrueNAS SCALE (now CE) server and an ancient Primate NP5 DLNA device. The NP5's DLNA implementation had some issues which didn't seem to affect Jellyfin but the device would not work with Emby. I was able to borrow a different DLNA device so that I could evaluate both Jellyfin and Emby (and briefly, a few others) over the course of a couple of months. At some point during that time I had to return the borrowed DLNA device and so had to use Jellyfin exclusively for a few weeks.
What I found in Emby was a well thought out and consistent and reliable media server and with few, if any, rough edges. Jellyfin in contrast really did feel more amateur,, clearly lagging behind in terms of basic reliability and features.
I reported the NP5 issue to the Emby dev team and they were fantastic, building in a workaround to that old and now obsolete device. They didn't have to do that. The result is that Emby has been reliably working in my system since then and I use it every day.
I immediately bought a lifetime licence in order to support further development and show gratitude.
Open or closed source, free or paid does not define the quality of a software product. There are good and terrible examples of all of those. If someone's value system directs them to use open source software exclusively then that is of course okay but that means nothing about software quaity. Ditto if someone prefers paid software instead of free.
What it comes down to is the quality of the product, regardless of whether it's free or paid, open or closed source. For me, Emby wins easily. Jellyfin's popularity is baffling; it's mentioned so often by people when Emby is far superior. Seems like ideology instead of objective analysis is dictating decisions and that is never a good thing.