We have restored the sidebar link for “My Posts” back to how it was previously:
https://github.com/discourse/discourse/commit/294ed87a6f5548ab031d31b85e4f559dcc8c8cdb
If you have added any additional custom links as a workaround to access the “My Posts” page, such as /my/activity/ (ie. with the trailing slash) then you may want to remove the custom url to prevent duplicate links.