Currently it appears only the title can be used as the entity label. The label method was introduced here: #2558143: Opt-out from optional base fields →
Many custom entities don't need a title field but may have other suitable fields which can be used as the label. If there's already a way to do this in the UI then I've missed it completely. The Title property/field seems to be left over from the pre-entity node days and is entirely optional with entities. Entity Labels aren't (or shouldn't be) optional and are more flexible.
Somewhat related, but it could also be good for the ECK content list ( /admin/structure/eck/entity/entity_type ) to have a Label column instead of Title by default.
Could this be done on a per-bundle basis? For example, we could list all the fields of type "string" as potential candidates, as well as the title if it's enabled.
Needs work
1.0
Code
The change is currently missing an automated test that fails when run with the original code, and succeeds when the bug has been fixed.
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It's likely this issue predates Contrib.social: some issue and comment data are missing.
Haven't scrolled the issue yet but please keep an eye on the core and AEL issues raising and getting progress regarding base fields. I think it is important to sync overlapping efforts here.
Too many to link them all here but some out of my head: #3088103: Entity label (title) field shouldn't be a base field but a required option to choose a field for. →