I tried to find some in-depth information on how to create a dashboard.py file for doctypes in custom apps. I could find some basic info and youtube videos on this topic. However, no in-depth tutorial.
Do you mean the dashboard of the doctype just like the Item doctype dashboard ?
If so, then you could take a look at the Item doctype source . There is a file “item_dashboard.py” there and it’s a kind of definition only and frappe will do the rest as long as the link is correct.
I’ve done this modification many times in doctype dashboard and indeed it’s quite easy.