I am trying to understand what happened if a website is having multiple customisation and third party plugin involved and 8+ years of data in db and then if we try to migrate it to CE.
I guess we can do it in 2 ways –
One is to run composer require command with CE+version (same as we upgrade) and then fix db using some sql queries for entity_id to row_id and then remove all licence files then remove extension related to EE.
Second approach is to install a open source of same version as EE Then move extensions and custom modules one by one to check their compatibility
Then plan on data migration like use magento data migration tool or custom scripts
Not sure that in downgrade edition the magento data migration will work or not.
What should be the exact approach with proper steps?