Hi Stefan
As a long term user and tweaker of Forms can I give my (possibly to be corrected by wiser heads) view
By .xml I am assuming you are meaning the likes of the custom.xml file
Which is essentially a slightly modifiable template allowing data entry in a standard format into the main database. It does not in anyway store your data (a mixture of human readable and data blobs).
Baptisms, Marriages and Burials I have found a particular problem in that you cannot attach Notes and any Media you attach via the Form does not appear when you go to the Individuals Event View and look at the Gallery you have to go via the Form which is not always convenient.
There is a member of this email group trying to develop improvements
worth a look
[Gramps] [Development] Plans to Update Forms Addon Over the 2024 Summer by Renee Schmidt
phil