I haven't seen any other reports of the RJ not being functional in MSFS 2024 post SU3, so this sounds like it may either be an installation-related issue, or a conflict with another mod/product.
The first thing I would recommend is completing a fresh reinstall of the product. Uninstall the product, download a fresh copy of the latest installer from the store you purchased from, and then run the installer through. Then launch MSFS 2024 and see if that has resolved the issue.
Note, we have also just released RJ Professional v0.1.4, which updates the RJ to a fully native MSFS 2024 package: https://community.justflight.com/topic/7294/rj-professional-changelog-updated-28-08-25
If a reinstall hasn't resolved the issue, then I would recommend trying a flight in the RJ with an empty community folder (except for the RJ). The best way to do this will be to rename your Community folder to something like "Community.old" and then create a new one named "Community" and run the RJ MSFS 2024 installer, that will allow you to test this with an empty Community folder and then revert back to your old Community folder without having to reinstall everything. If the RJ works without any other mods/products in the Community folder, then that likely points to a conflict.
If the above solutions don't work, could we kindly ask you to raise a ticket with Just Flight Support at the following link, and one of our support team will be able to assist with further troubleshooting: https://www.justflight.com/support
Mark - Just Flight