Version 2021.3.0 introduced the concept of trigger_variables. However, at this early stage, they don’t support everything that can normally be done with a Jinja template. The documentation refers to this reduced templating functionality as “limited templates”. It explains what it doesn’t support and it’s quite extensive. Basically, “limited templates” let you define constants and not much more than that.
FWIW, I had submitted a Feature Request months earlier and subsequently reviewed trigger_variables when it was first released