See How do I use a multiple keystroke trigger?
You can assign multiple macros the same hot key, and Keyboard Maestro will display a palette of the conflicting macros when you press that hot key. You can then use number keys or the mouse, or the first significant letter to select the desired hot key. This is especially useful when you have a variety of similar or related tasks. You can also assign a hot key to a macro group which can activate it for one action (with or without a palette), and the contained macros can have whatever ”second” hot key you desire.
A Macro Group can be activated for one action after you press an initial hot key (optionally displaying a palette of its macros), allowing you to specify any second trigger you like.
A macro can use the Activate Macro Group for One Action action to explicitly activate another macro group for one action, allowing any complex chaining of hot keys.
There is a Typed String trigger, which takes a series of typed characters and then optionally deletes them, but this is restricted to typed keystrokes, so no Control or Command modifiers.
And finally, macros can enable and disable other macros or Macro Groups, allowing all sorts of possible control.
But Keyboard Maestro does not directly support assigning a two-keystroke hot key to a trigger. The problem with multiple keystroke triggers like Option-F R is what to do if you type Option-F A?
Logic dictates that the Option-F A should go through to the system unimpeded, but Option-F R should be swallowed entirely. But this is impossible. The only way to do it would be to swallow the Option-F key, and then swallow the second key and then resubmit the Option F and the second key unless it matches Option-F R.
However, that is fraught with peril and cannot work robustly in the presence of other applications placing things on the keyboard event queue (or even a sufficiently fast typist).
For example, suppose you quickly typed Option-F A B. Keyboard Maestro would have swallowed the Option F and then the A, and then resubmitted it to the event queue, resulting in the stream of characters B, Option-F, A. There is no way to avoid this race condition, and as such Keyboard Maestro does not support any such mechanism.
As described above, Keyboard Maestro has a variety of ways you can use Option-F as a hot key that allows a second key to be used to select a macro. However in all cases it is clear that the Option-F has been used and there is no concept that the Option-F might come back later to do something else.