The Joplin basic custom time/date variables are date, time, datetime, bows, bowm and are enclosed in double curly brackets i.e. {{datetime}}. They display the date / time format as it is set in Joplin's settings. These cannot be used in {{#custom_datetime}} tags.
Well, I would like to use a custom variable (data_pagamento: date), so I would be prompted to enter the date when adding the template. But I would like to make this presents the date in the format DD/MM/YYYY, and not YYYY/MM/DD as it is doing now.
I see! Sorry, it seems that I was referring to something different
The {{#custom_datetime}} variables will set the date at the time the note is created only. Basically it is an alternative to the template plugin's "built in variables"
You are right, there does not appear to be a way to change the date format when using the template calendar dropdown / selection tool. Although my selection calendar shows the date as DD/MM/YYYY when I select it, it creates the date in the note in ISO format YYYY-MM-DD.
Just looked at the Plugin's GitHub page and it seems that an issue has been raised about this.