The help file indicates the second parameter can be a picklist, but that is all. To input into a link field, you can either do freetext input, or a picklist.
Other field types will adapt the prompt to their type:
Given this, I think this would make a great feature request to allow the Prompt on a link field to also display the Associated Item Selector. I've placed the details about how to log a feature request below. Please post the link to the request after you've logged it and I can throw my vote at it for you too
The functionality that you are looking for is not currently available in the product. Our product management teams are always looking for new ideas to help us improve our products and we know the best ideas come from customers that use our products every day.
We would therefore encourage that you consider submitting a suggestion in our Feature Request portal via the Ivanti Community Ideas homepage
You can submit ideas and show support for ideas that other customers have submitted by voting for them. The more votes an idea receives, the more visibility it receives with our Product Management team. The Product Management team will evaluate all ideas that reach a voted point threshold. When there is an update on the status, an Ivanti product manager will reply to the idea or update the status so that all interested parties are notified. It is therefore key that you as a customer raise new or vote on exiting ideas to be kept looped in with future progress.
When you create an idea, please describe both the problem or pain you're experiencing as well as your suggested solution to that problem. It can also be useful to describe specifically how you would use the new feature if it were built, as well as how you are dealing with the problem today. The better your explanation and logic, the better your chances of attracting positive votes from other users and ensuring a response from Product Management.
Thanks in advance for your feedback.
If you have any other comments or questions please do not hesitate to contact me.
Ivanti Community Ideas Homepage: https://community.ivanti.com/community/enhancementrequests
Couple of options, use a pick list but the value field has to be the RecId of the value you want in your link the following example completes the profile link in Incident:
The other option is to not use a pick list and use a drop down field instead and create the field relationship from the _valid field to the otherobject table.