Cannot resolve type problems with eclipse

It seems that I got the wires crossed & ask you to point me the right direction.

I have a problem with the Eclipse IDE for Enterprise Java Developers (version: 2019-06 (4.12.0), build id: 20190614-1200). There is a code part where I get the error message MysqlDataSource cannot be resolved to a type. Searching the Web, I found out that this class is included in the download of mysql-connector-java JAR 8.0.14 with all dependencies. I added it over the 'Fix project setup…', where I added the JAR file to the libraries of the Java Build Path. Unfortunately, the error message does not vanish. Can you see what I am doing wrong?

Edit 1: With the hint from another Website, I found out that the hibernate JAR included was the source files JAR. So, I corrected it the hibernate-entitymanager JAR, clicked "Clean…" under "Project", but to no avail: the EntityManager is still unlocatable. (Well, after several tries, the first error message to resolve is no more with MySQL.)