There is no supported method to downgrade an Odoo database.
You may be able to export and import data but would need to do this one model at a time and have a full understanding of related models and schema differences.
It would be a time consuming, frustrating and error prone process.
Hi,
I'm looking to do exactly the same. I hope someone has a solution to do this.
We need to downgrade to get the better version of Odoo instead of the terrible upgrade version.