As the VCP docs state, you should uninstall the plugin first, and install it anew after an upgrade.
Now some surviving bits and pieces that try to use vCenter 6.5 are still in there, but VCSA 6.5 is gone.
You need to use the troubleshooting procedure from the VCP docs to manually clear orphaned/stale VCP files (it's a find + delete combo for "*solidfire*" files and directories, IIRC - check the UG). Log out from VCSA Web UI, execute that step, then go back to mNode and re-install. Maybe a VCSA reboot would be required.
Since the plugin is not functioning, you might as well use this opportunity to install the latest mNode before the last step (VCP re-install) and that would help you install a newer VCP (which contains minor improvements and bug fixes).
If this sounds too complicated, it may be best to contact Support for a review of the exact steps.