please try this

there are two ways:

first Way
def name_get(self):
result = []
for rec in self:
display_name = f"[{rec.field_name}] {rec.field_name}"
result.append((rec.id, display_name))
return result

second way
def name_get(self):
record = []
for record in self:
record.append((res.id, '%s - %s' % (res.field_name, field.field_name)))
return record