Hi inskiv29318254 ,
Preflight profiles, checks and groups are now grouped into different libraries namely "PDF Standards", "Essentials" and "Prepress, Color and Transparency".
PDF X-3 and related profiles are present under "PDF Standards" library. For switching libraries, Just choose “PDF Standards” from the Libraries drop-down present at the top of the preflight dialog.
You can also use the Search all libraries option for searching the desired profile across all libraries.
For more details, refer Preflight Libraries (Acrobat Pro) .
Let us know if you have any concerns/feedback.
Regards,
Priyanka Jain