A simple hack solves the problem of Shotcut not supporting subtitles.
In all instances in my experience, Shotcut would not show or read the subtitles I’ve already placed inside a video using external programs. Thankfully, I’ve found an easy way out of this nagging issue:
CREATE SUBTITLES for your video.
I use a totally free, no-watermark & no-need-for-registration program called “SUBTITLE EDIT” version 3.6.11. Others use Aegisub, but I’m not familiar with it. Subtitle Edit has a command that generates auto-subtitling (even in languages other than English) after dragging your video in it. Though not 100% accurate, but the timing are almost there, and you simply tweak easily the generated subtitles to suit your needs. Result: a subtitle .SRT file, which you’ll need in the next step.
HARDCODE THE SUBTITLES to your video using VLC’s Media Streaming command. Result: an MP4 file with hardcoded subtitles. Google the tutorials on how to do this.
Try opening the new VLC-generated MP4 file in Shotcut and voila! You can now see your subtitles.
(Previously, I used MKVToolNix to hardcode subtitles in step 2. It’s faster and easier than the VLC. But Shotcut won’t read its generated subtitles. Also, its resulting MKV file is about 250% bigger than the MP4 that VLC generates.)