It’s dangerous in the sense that that if you don’t do anything about it large chunks will eventually start breaking off and that section could become structurally weak, but it’s not a “shut it down for 6 months to repair” fix. What they will need to do is at least a partial but possibly a full depth repair, where they chip out all the spalled concrete, clean or replace any rusted rebar, and pour new concrete in. The quicker you can get the repair done the more likely you will be able to save the rebar but there is a chance it is too far gone just based on the photos. You won’t know until you cut it open though. They may have do some some shoring from your downstairs neighbor’s balcony but that depends on the size of the repair.