MySQL InnoDB foreign key between different databases

It's possible : Link to do it

Example (Table1 is in database1 and HelloTable is in database2) :

ALTER TABLE Table1 
ADD foreign key FK_table1(ColumnNameFromTable1)
REFERENCES db2.HelloTable(ColumnNameFromHelloTable)

I do not see any limitation on https://dev.mysql.com/doc/refman/8.0/en/create-table-foreign-keys.html.

So just use otherdb.othertable and you will be good.