i already found out myself
just replace <@ title @>
with:
<@ if @{ customTitle } ~@>
@{ customTitle }
<@ else @>
@{ title }
<@ end @>
this creates a new variable in the template settings. there you can add a <br> tag.
i just understood that when i add a <@ variable @>
somewhere template code, it will generate a new variable in the template settings. 😅