
MarikitG.68627 (Customer) asked a question.
For example you got a custom attribute "behavior" in app user profile. How can I retrieve the value in email template? is it $appuser.profile.behavior? I have tried it like this and its not working. Am i missing something?

I would like to direct you to the following question that seems to really match your request as well:
Using user attributes to customize email templates
Within this, an Okta employee answered that there are in fact only a limited subset of all available Okta attributes that can be used in a custom email Template. The list is available here: Expression Language for Activation templates
Unfortunately, based on my own limited testing, it appears to still be quite accurate. When modifying with user.email, it worked flawlessly but when using some other, not listed, custom attribute, it failed.
I am sorry to say it doesn't look like it is supported yet. You can always submit this as a suggestion on Okta Ideas where we can vote on it with hopes it will be in a future release.
Hope this helps! Thanks.