Please note: the "port for Drupal 9" ticket was not complete in this release. You will be unable to install any of the sub-modules, because the new core dependency format in the info file was not updated for the sub-modules.
RC3 addresses deprecated drupal_set_message() issue. This means that there is a minimum version of 8.5.0 core. If you are using an earlier version of D8, please use RC2.
There is a critical bug in the token refresh code, please apply Patch from #2978219.