If you use the SDK, a new Eclipse (version 2020.06 or higher) is recommended. If there are still dependencies to the old org.apache.log4j plugin, you should create a new workspace for Eclipse.
solved the problem starting from a new Eclipse environment (2020-06) and clean Workspace.
Great, we have by the way recently found that 2020-09 causes issues using the SDK and will investigate into it. But since you have taken a slightly older one that should not be a problem.