Mysql Error:The user specified as a definer (‘mysql.infoschema’@’localhost’) does not exist’ when trying to dump tablespaces

I had the same error when I accidentally downgraded my MySQL version from 8 to 5.7. At the first start the older version broke something so that version 8 was showing the error above.
In my case I had to enter the docker container where MySQL was running first

docker exec -it mysql bash

Then I basically followed the steps here

mysql -u root -p
mysql> SET GLOBAL innodb_fast_shutdown = 1;
mysql_upgrade -u root -p

This took some minutes but then everything was working again.