Good question.
There were previous questions / discussion of this before (2013 - 2017):
1) https://www.odoo.com/forum/help-1/question/where-is-the-workflow-chart-of-odoo-standard-modules-55684
2) https://www.odoo.com/forum/help-1/question/business-processes-flowcharts-113896

In previous versions there was an option to turn on "Technical features" (up to v8) for a user (through user access rights) or turn on "Developer mode" (starting from v9) to get a diagram view (workflow charts) for each module.
The evidence of this can be found here:
https://www.odoo.com/forum/help-1/question/where-is-the-workflow-chart-of-odoo-standard-modules-55684
...and here:
https://www.odoo.com/forum/help-1/question/how-to-activate-the-technical-features-7650

Question update:
What's the current status of this feature?
How to get the diagram view?

Another question:
Did anyone come across any standards for processes description in Odoo community?
I am currently considering using of ARIS Express tool and EPC notation with one of the Odoo clients.
It would be nice to have the flowcharts / diagrams for Odoo modules on one side and the client’s processes “as is” on the other side to be in the same notation…

Any information is appreciated.
Thank you.