Problem 01
Subtitles
Personally, I like having subtitles on. But the only way to make them play consistently across devices is to have them hard-burned directly into the video file itself.
Solution
VLC Player — plays nearly any media file, and lets you pick a subtitle track on the fly instead of baking one in.
Problem 02
Casting
That only works locally — on the computer running VLC, or a mobile device running VLC. I tried casting VLC from a PC to the TV over the same network and ran into issues. Could be a TV software problem. Could be a VLC software problem. Either way, it didn't work.
Problem 03
Setup
Tedious to set up. You'd have to copy the file into VLC every single time — it isn't readily available. Even with the movie sitting on a cloud drive, you'd still have to import it into VLC, per device, every time you wanted to watch it.
Problem 04
Marvel Movies
I always wanted to have a day to binge the Marvel Endgame series. Unfortunately, when I had the free time it was difficult to find a good stream with good quality without intrusive ads. I mean, that is just the way it works if you want something for free.
Anyways, beyond finding a good source — I wouldn't even know what order to watch it in, and it would require setup per-movie anyways. Secondly, there was a time where I did subscribe to Netflix just to see they only have one part of a franchise, and HBO MAX having the other movie, etc.
That got annoying. So to get the true experience I would have to pay subscription for multiple streaming services when I literally only have 1 day free to watch movies. There have been months where I just pay Netflix and don't use it too.