Had to solve this problem at two separate places and boy was it a journey. The pigeons ignored everything, even the spikes; we later found one sitting in nest built directly atop of them, looking all cozy (place was unoccupied at that time). What actually worked was two things: a net and a cat. The net broke once after some strong winds, so needed maintenance, but otherwise works okay, albeit the ugliness factor.
The cat solution was a bit unintentional thanks to ... lets say involuntary adoption, but he takes care of problem with flying stars. The pigeons even seem to have started avoiding the place. This is on the fifth floor as well and he thankfully did not manage to yeet over the railing yet, though I wouldn't be surprised given how enthusiastic he is. We did weave a mesh through the railing in a measly attempt to reduce this risk.