I think you can actually use <br> for Calculated Values. However, you will need to enclose it with a single quote.
Refer to this syntax:
You can also use CHAR(13) which is a SQL Function called "Carriage Return" since Calculated Values accepts SQL statements.
Refer to this syntax for CHAR(13):
'[@field:Line1]' + CHAR(13) + '[@field:Line2]'
This will output the values like shown in the screenshot below: