This is almost certainly The Beast Adjoins, by Ted Kosmatka. First published in Asimov's Science Fiction, July-August 2020. No synopsis yet on isfdb, but the full story is available directly from the magazine website.
In the story, humans develop AI, with one strange problem:
They were given eyes to see and ears to hear. They were given voices to speak and
legs to move.
But none of that mattered.
Because while the AIs could create symphonies, and write dirges, and paint landscapes to make humans weep, there was one thing they could not do. They could not
interact with quantum systems. From a physics perspective, they were quiescent.
Just material.
They could see but not observe.
The solution that the AIs develop to this problem has horrific consequences for humanity:
Humans were captured and bound by the thousands at the end of long, silver
spines, hung over battlefields and across broad metal backs—screaming, crying,
begging, worn as adornment, and as ablative armor, and as holy totems.
Others were placed into metal racks at the front of the great machines, casting reality for the AIs in the same way a headlamp might cast the world before a speeding
train.
“Captured divinity,” the AIs declared. “God in a cage.”
This is actually all backstory, interwoven with a plot set much further in the future that I won't spoil for the sake of new readers.
The story appears to have been made freely available as a pdf, directly hosted on the magazine website - I think in conjunction with this Wired story from last fall.
