Set Columns as Hidden or Read-Only
BoostSolutions' Column Permission App enables you to set columns as hidden or read-only for specified users or groups in SharePoint Online lists. This helps restrict users from accessing or modifying certain columns in new/edit/view item forms or in list views.
(Note: The app only works in the SharePoint Online modern experience.)
Set Permissions Based on Condition
You can set column-level permissions based on the values of other columns, making it easy to determine when and if columns should be invisible or read-only.