If you read the user manual, it recommends 93 octane for peak performance and states 87 octane is fine. I had a 2019 6.2l and only ran 87 octane with no issues (recently upgraded to a 2500). Car and drive had an article back in 2016 I believe where they did dyno runs on a escalade with a 6.2l with both 87 and 93. With 87 it lost ~20hp is what they found. So if you are okay with a little power loss, you should be fine.
So basically both 87 and 93 are safe, but your engine is changing timings while running 87 resulting in power loss