You should try the COMMENTS REPORT plugin which is part of the free abracadabraTools :
https://www.abracadabrapdf.net/utilitaires/utilities-in-english/abracadabratools_en/
It can be customized (I can give you the source JS file) to works with Acrobat Pro, so comments will be exported as a new “Report”, which is a regular PDF file.
See:
https://opensource.adobe.com/dc-acrobat-sdk-docs/acrobatsdk/html2015/Acro12_MasterBook/JS_API_AcroJS/Report.htm?rhhlterm=report&rhsyns=%20
&
https://opensource.adobe.com/dc-acrobat-sdk-docs/acrobatsdk/html2015/Acro12_MasterBook/JS_API_AcroJS/Report_methods.htm?rhhlterm=report&rhsyns=%20