MPV is pretty much a gold standard for video players, it’s a bit more keyboard focused, but basic functionality is fully accessible through the GUI.

But I don’t think VLC should struggle with embedded subtitles. Maybe you can feed your video file to ffprobe and share the output for a bit of troubleshooting?

I had some issues with mkv files on VLC a few weeks back (same files worked fine in Haruna), but they seem to be working ok for me now.