I should probably add that our unit is the end one with stairway facing the street.

A beautiful fall wreath on the door, 1 nice size mum on each side of garage door in nice pots ( could be clay pots), plant mums in your beds, do a grouping of mums/ pumpkins at different heights in corner of porch.
Kale (looks like cabbage) looks nice planted in beds.
Look at landscaping magazines for ideas for your beds using kale and mums.

Being a condo you probably cannot plant, either. How about a pot on each step either mums or cabbage/kale?

Corn stalks and pumpkins are always fun. A basket of gourds by the front door. A hay bale. Do you like yard flags in seasonal themes?

There are great ideas above. I've lived in a condo and we could plant, but it sounds like you are looking for fall decor.

I'd do a nice fall wreath on the door. You could look into faux berries & leaf garland to wrap around the posts & banister. Depending on your budget & storage space, I've used faux foam pumpkins on my porch stairs in a descending fashion, larger at the top and smaller at the bottom. Not every step, but maybe every other?

I also like the ideas about colorful pots with annuals or mums. If you can plant, then you could put the mums in the ground.

Depending on the condo rules, some string lights in orange would be cute on the tree if you like to get that festive for Halloween. You could wrap them on the top rail of your deck as well.

I've been told by neighbors that the association is pretty lax on planting. So I might consider popping in some mums and kale for the season. Keep the ideas coming, it's really helping me pull together what I already have and determine where to put it.

Here you go....

Here's another....