With Tomcat9 on Ubuntu 20.4, there is not tomcat8 user but tomcat only.
So, I created tomcat8 uerr, added it to tomcat group, and added good rights (rwx) to /opt/collab directory.
drwxrwxrwx 5 tomcat tomcat 4096 Jun 18 11:19 collab/
But i get same error "An SQL data change is not permitted for a read-only connection, user or database."