You are in PR 2020 or earlier. The workflow changed substantially for PR 2021.
You are in the Captions Export Settings, but this is not where you do the export.
You can export srt 3 ways:
1) File -> Export -> Media: When you export the sequence, use the caption tab in the export dialogue.
2) Select the caption stream in the Project Panel and File -> Export -> Captions: This will give you the timecodes in the Caption Panel, without changes made in the timeline only.
3) Select the SEQUENCE in the Project Panel and File -> Export -> Captions: This will give you the timecodes in the Sequence, even if you have chopped up the caption stream.
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