QuickBooks Online does not let you give access to only specific reports. The permissions are tied to the user role, so once someone has Reports access, they can see most reports in that area.

The closest workaround is to set them up as a Standard user with limited access to only the customers or vendors they need. This limits what they see inside many reports, but it will not hide the full report list.

If you only want them to see your custom or memorized reports, you will need to export those reports to PDF or Excel and share them outside QBO, because QBO does not support report-level permissions.

It is a common request, so you can also submit this through Gear > Feedback so the team knows it is important.