Git client plugin 6.0.0 includes JGit 7.0.0. JGit 7.0.0 has removed many API's that were deprecated for multiple years. One of those removed API's is setForce(boolean). That API is used by the maven release cascade plugin in its checkout method. That method will fail if used with git client plugin 6.0.0 or later.

The workaround is to use git client plugin 5.0.0 or earlier.

The fix will require that someone adopts the maven release cascade plugin and updates it to replace the setForce(boolean) method call with its replacement, .setForceRefUpdate(true)