@Gatlingorange
Well, I've tried entering the STAR and runway mid-flight, but unfortunately, that didn't help either.
I could see the TOD marker, and after ATC confirmed which STAR and runway I should use, I entered them into the CDU. I then selected a lower altitude and pulled the altitude knob. IMM DES became active, but after activating it, I ran into exactly the same issue as before.
I've also completely reinstalled the simulator after Sim Update 7, as well as the F70 and F100, but I still can't get it to work.
I'm honestly running out of ideas, and I really don't know what I'm doing differently from you.
If it's not too much trouble, would you mind giving me a step-by-step explanation of how you do it? I'd really appreciate it!