You can see in this example the user has Burn Captions Into Video selected at first, with the captions showing on the video preview to the left. Further back in this example, the Subtitle track is still shown (not hidden) in his timeline. Once Create Sidecar File is selected, the video preview then removes the captions and the user is able export the video without the captions burned in and get an accompanying .srt file, quickly and easily.
This is how I used to work with captions for the longest time. I was able create a caption file and edit in my timeline with the captions displayed all the way through the export process. I was able to go to the export window and choose to create a sidecar file, which would then HIDE the captions and do exactly what the setting says, creates a sidecar file for me instead. So I would have a video file and an .srt file, done.
My issue now is that this exact same workflow seems bugged with the newer export workflow. The Burn Captions Into Video seems to be inherently always checked. If you choose Create Sidecar File, the captions are STILL burned into the video. The only way I'm able to turn this off is to go back to my timeline and hide the caption track (you didn't have to do this before!). Hiding the track however, disallows you to select the Create Sidecar File option in the export window. You have to export the .srt file separately from the timeline OR render the video twice, once with the caption track hidden, and then again with video/audio hidden to create the .srt file.