Here are some reasons why you might not be seeing your lookup field:
1. Missing a linked record field
If you do not have the linked records field on the form, you will need to add it. Lookup fields can’t work (display data) without a linked record field in order to be populated.
💡You can disable editing for any field in the form (including the linked record field). So it would be read-only.
2. No linked record selected
The linked records field does not have any linked records selected.
3. Lookup field has no value
The linked record you selected does not have any values for those lookup fields.