Hello,
You can send email notifications in HTML format with the help of a PowerShell script.
Use the Run a program or PowerShell script action instead of the Send e-mail notificaion action.
Here is an example of a PowerShell script that sends e-mail notifications:
$toAddress = "%mail%"
$subject = "Hello, %username%"
$bodyText = $Null
$bodyHtml = "<b>Dear %fullname%</b>"
$Context.SendMail($toAddress, $subject, $bodyText, $bodyHtml)