Looks like this is your first post…welcome! This is a GREAT community where the people are very willing to help out. You’ll find great info and camaraderie here.
Stream Deck itself might be able to do it for you using the multi-action feature. Inside of that multi-action you could place two “hotkey” actions, the first being the ALT key, the second being the F1 key. I haven’t ever attempted this myself but it’s worth a shot, and it would perhaps keep things simpler.
However, it might be possible with Keyboard Maestro too. Simply use the “keystroke” action with the ALT key, then another “keystroke” action with the F1 key. You may need to insert a pause between those two actions depending on how FGU responds. Note that Keyboard Maestro even has the ability to send those “keystroke” actions directly to a specific application, but not all applications register them like they would if they were manually pressed, or pressed from within the app itself.
So that’s two options you could try, though I can’t guarantee either one will work haha. But try them out and report back if they don’t and somebody way smarter than me might come up with something better for you.