The CRW End User Guide suggests that using Intellij is supported within CRW.  (See sections 5.6 - 5.7.5 [1]).

We do not yet offer support for Intellij.  There is a Jira [2] that aims to provide it, but it's not scheduled until 2.11.

Please remove sections 5.6 - 5.7.5 until Intellij is fully supported

[1] https://access.redhat.com/documentation/en-us/red_hat_codeready_workspaces/2.9/html-single/end-user_guide/index#using-alternative-ides-in-codeready-workspaces_crw

[2] https://issues.redhat.com/browse/CRW-1358