I just wanted to give a heads up that the system I work with (and I suspect it might not be isolated to that) has MySQL database collation incompatibilities when the database is exported/imported to MySQL version 8.
I experienced this problem locally, and the customer is experiencing it on their SugarCloud upgraded test system.
It might require collation changes completed for every table/field, as I executed it locally on my own environment to get it to work.
The error messages received in the Sugar log will look like this:
EXCEPTION An exception occurred while executing a query: Illegal mix of collations (utf8mb4_general_ci,IMPLICIT) and (utf8mb4_0900_ai_ci,IMPLICIT) for operation '='
And the API request fails with an http 500 error.
Hope it helps give you some hints with the platform upgrades!