To my knowledge, it's not just the CONCAT operator that doesn't accept line breaks, there's no operator that enables the insertion of a line break into a calculated expression.
The only way in which calculated fields end up containing line breaks is when the expression that writes the calculated value references a text field whose value already contains line breaks. E.g., consider a simple expression that is just CONCAT({description}) on a calculated field called DE:Calculated Description. Since the description field of an object allows the user to enter line breaks, any calculated expression that references description will honor the line breaks in that field when it copies the text to DE:Calculated Description.
With that in mind, one could:
1. Create a custom text paragraph field called DE:Line Break and add this field to a custom form that is attached to the instance's primary Company.
2. Edit the Company's custom form, and in the DE:Line Break paragraph field, enter some invisible unicode like 200B 000A 200B (zero width space, line break, zero width space).
3. In the CONCAT expression on the field in which you need to insert line breaks, reference {company}.{DE:Line Break} between the strings that require a line break.
I have tested this approach and it works, albeit clunky.
The intent of adding the DE:Line Break paragraph field to the Company object, as opposed to a project/task/issue object, is it allows you to centrally manage the field and ensure it has the correct unicode values. Users don't even know it exists much less have the ability to overwrite it, and admins only have one place they need to manage it.
I don't know why I hadn't thought of this before, thanks for the challenge!
-WE
