When you give users access with read-only, no details permission, events will show very limited information:
All other event fields are hidden from view.
When you give users access with read-only permission, events will show with all event details, including attachments. Users will not be able to change the events, but they will be able to see all field contents, links, and access any attached files.
In some cases, you may want calendar access that's in-between these two options. For example, you may want users to know who's been assigned to an event, but hide all other event details.
Here are two options to consider:
For example, to show who's been assigned to an event, create a sub-calendar for each person (potential assignee).
Make sure these sub-calendars are included in the read-only, no details access for the users who need to see the assignment.
Then, assign events to the relevant person's sub-calendar (in addition to other sub-calendars needed). Since sub-calendar titles are visible even with no-details permission, the users with will be able to see the sub-calendar name(s) and know who's been assigned.
Enable event comments and make them visible to users with modify permission only.
Users with read-only or add-only permissions will not see the comments, so they can serve as internal notes or hold information you want hidden from these users.
See also this workaround to show event titles only and keep other details hidden.