The GP tool for assigning domains to field should list existing domains in the GDB. Manually typing in a name and hoping it matches is a point of failure. This is why we have domains in the first place.
If you or @LindaWilliams1 could let us know what version of ArcGIS Pro you are running and under what circumstances you are not seeing a dropdown pick list in the tool, that would be important to understand.
Because the tool's documentation(this is from 2.6) indicates that 'Available domains will automatically be loaded' and when I look in 2.7.3 I see a pick list, this is not actionable as an idea.
If there is a specific problem with data set up, or something else that is going on that causes the picklist to not display, further troubleshooting will be required and a bug potentially logged.
Please provide more information so that we can determine if there is a valid idea here, or if you will need to troubleshoot with technical support.
When assigning a domain to a field with the GP tool I have to type in the domain name. I would expect the GP tool to recognize which GDB I am sourcing and list the existing domains.
Typing in the domain name can lead to data entry problems.
Thank you for the comment, but since the Assign Domain to Field tool already provides a pick list, we can't move forward with this idea in its current state.
My guess is that because you're working in a model, perhaps something upstream hasn't been created yet... I can't be sure, but you will need to troubleshoot.
If you can provide anything else that might clarify the idea, please do. But for now I don't see this idea as being valid. @LindaWilliams1 since you voted for this idea, do you have anything to offer that might help us understand when the pick list is not presented in the tool?