We discussed in the previous post: https://storejextensions.org/forum/view/10-jsitemap/7389-re-duplicate-title-tags-and-meta-descriptions-in-google-search-console.html
Obviously the issue is not caused by JSitemap, it doesn't generate duplicated title tags, it simply offers the Metainfo dashboard system to override them if needed, this is shortcut to solve quickly the problem of duplicated titles.
And the Metainfo Dashboard must save values that you enter them and click the 'Save' button, it's not possible that values are not saved to the database.
If you want to disable completely the Metainfo dashboard feature and test any change, you can unpublish the plugin 'System - JSitemap utilities'.
Other than this you could have other extensions installed that manage Joomla titles/descriptions.