The "Link to" field shows the fields in the edit/detail form. In fact, in the example you can see the title. When editing the Add task form it is not possible to show the fields, thus making selection difficult.
The two forms should have the same possibilities, I believe they are not aligned.
Yes, unfortunately, this is a known limitation of Airtable.
Be sure to send an email to firstname.lastname@example.org to request that this functionality be improved in the future.
In the meantime, the workaround for this is to make your primary field in the linked table a formula field that shows you all the information that you want to see.
The other workaround for this is to use Fillout’s advanced forms for Airtable, which solves this problem by letting you choose which fields (including attachment fields) that you’d like to see when selecting a linked record.