The spikes on Steppenwolf's armour disappeared when Darkseid appeared before him:
Why did this happen?
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It's a symbolic show of deference, which reflects his humility before and fealty to Darkseid, similar to those shown by our knights.
In an interview with Yahoo Sports, director Zack Snyder said,
"He's a legit space knight."
and WETA Digital Visual Effect Supervisor Anders Langlands added,
"Zack had the idea that his armor would react to his mood and be part of his performance, as if it was some kind of alien technology that’s symbiotic with him."
So the armor is reflecting Steppenwolf's deference to Darkseid.