Obviously, Agenda uses the Scribble feature of iPadOS 14+. However, there is an auto correction built in, even when auto correct is switched off in the iPad settings. So, when I tried to handwrite “Bild”, which is the German word for “picture”, it was changed to “Bill” - hm.
When rummaging about for a solution - by the way, there is not yet a proper one - I found a little work around, which is not perfect, but helps at least with frequently used words:
Hope it helps