Notification: Missing Linebreaks in HTML formatted Email

Hello

I want to send email notification including the full_message field which contains line breaks.
When sending email notification as plan text, the line breaks exists in the email.
But when sending in HTML format these line breaks are missing. Reason: line breaks must be replaced by the <br>-tag.

I want to use the replace function but without success:
${message.fields.full_message?replace("\n", "<br>")}

My Environment: Graylog 6.1.2+c8b654f on graylog (Eclipse Adoptium 17.0.13 on Linux 5.4.0-1135-azure)

What can I do?
Thanks for the help.

Can somebody help me? Is there a Replace function which can be used in the template?