TheMarvinX,
I cannot thank you enough for your post!!!
I have been suffering 2fps and limited by rdrthread a few weeks after SU6 as well.
I have tried many hours of troubleshooting the problem, updating/reinstalling the graphics driver, tweaking MSFS graphics settings, removing files from my community folder, multiple re-installations of MSFS2020, upgraded to Windows 11 all to no avail!
I uninstall citrix and boom!
Problem solved!!!