For the heck of it I just dug out an old Xbox 360 controller for Windows. It has a special USB dongle of its own so that the connection to the controller is wireless. Unlike the Spektrum dongle, plugging in the Xbox dongle alone didn't make Windows see any kind of game controller, but once I turned on the Xbox controller, Windows saw that and RF was willing to start. FWIW, RF assigns a generic "Gamepad" controller profile to an Xbox controller. It feels pretty strange using an Xbox controller with RF, but it can be done!
I also tried a set of rudder pedals I use with MSFS. That also works and gets RF to run! It would have taken a few minutes to figure out how the controls are mapped; the plane in RF spun and crashed pretty much immediately.
So yes, any Windows game controller device should make RF happy. If you can see it listed in joy.cpl in Windows (the Game Controller control panel applet), then RF should start.
I found some really cheap USB game pads on Amazon starting at $9.99.