Question is, where does the URL originate from?
A URL is just a string with a specific format.
In the open link button you do have 2 options
I hope the first doesn’t require explanation.
The second is based on a string type attribute. An attribute is part of an Object and a Object is derived from an entity.
Thus if you want to use the dynamica value; this button must be placed inside an Dataview, with the datasource connected to the entity, which contains the attribute capturing the URL.
What the source of the value of the URL is; I don’t know, that depends on the app process.
Please read this document ref: https://docs.mendix.com/refguide/page-properties#2-3-6-url
You can add a URL in Attribute on the Default value, see on the image, and pass this attribute on your button make sure to use your button on data-view.
Try this if it works for you.
You can select url attribute form here
I have used this concept. But in that scenario in the edit page, I had put any value in the address attribute and sent that attribute in button in list view. Like below
You will need to wrap your button/link in a data view, and use the entity and attribute which contains the URL you are referring to. Otherwise the “Use attribute” option wont have any context.