The new graphics export is great, but it is not intended for import to third party platforms for subtitles.
Here's the Youtube help page:
Bottom line; you really need an srt file.
I can't work on this now, but there is probably a way to reformat the graphics text output so it is in srt form. SRT looks like this:
00:00:00,000 --> 00:00:03,136
Caption 1 text
00:00:03,136 --> 00:00:04,637
Caption 2 text
If your piece is short, I suggested this (slightly outrageous) option to someone the other day: Record the words being spoken as they come on the screen. Add that audio as its own track. Use the speech to text and create captions. Export srt.
A new PR feature is that you can take those captions and convert them to graphics text. But the opposite (what you need with your current workflow) is not there (yet): convert graphics text to captions.