Lock a Field on a Record based off of Profile

Question

I have a field on a record that should only be editable by people with a certain profile. I can see that the read/edit is selected correctly under the field level security and I can see under the profile object settings that the field has read/edit access. There are no validation rules on the object that would block the access to the profile on this field.

Is there another way to completely lock down the field that I am unaware of?

I have looked at RecordTypes, Triggers, WorkFlow Rules...none of them touch this field. I am pretty stumped, is there another way to lock a field top level down?

Total SU is the field and as you can see from the pictures there is read/edit access from the profile object settings

here you can see that the field is entirely locked.

and from the field level security you can see that the profile doesn't have "read only" checked

Answer 1

There's two ways to block an edit on a given field and display that "lock" symbol you see (in Classic).

1. You can set the field permission to "read only" as you mentioned for that particular profile

2. You can mark a field as read-only on the layout level for that profile

Regardless of the profile permissions from #1, the layout will lock a field in the UI if you select it as "read only"

And you'll notice on the layout editor that the lock symbol now appears next to the field

Any user in a profile that is assigned that page layout will now be unable to edit the field. Important to note: this doesn't apply to API/Apex edits to that fields as the layout restriction is strictly enforced in the UI on the record.