In your email template
add text with the link type
and replace with your deep link
You need to have a token that you will use inside your email template, and in that token, you will store the generated link that you need depends on your configuration, also you can use Application URL java action to get your application root and to generate the link depends on your environment link and concatenate it with your your deeplink name. so generate the link then replace it inside your token attribute.
Create a button on your email template and pass the deep link URL as a token. It will work. Added screenshot for reference.
Once you can see the button in UI just double-click the button the LINK popup page will display.
In that, we can able to see the URL.
use this icon to replace the deeplink