You may run into issues getting it authenticated. With RF being sold to Horizon, they changed distribution to Steam, rather than selling CD's. There were/are plans that the server that authenticates licenses will be shut down. Go to the RF forums for more information. A call to Horizon may be needed, if it doesn't accept your license.
As for Win 11, my 8.0 version has had no issues, but was installed before the above change. There hasn't been huge changes in the core code since 3.5 (features, yes, many), so it should just work. Worst case is that you may have to tell Windows 11 to install it in compatibility mode for an earlier version of Windows.