I found a bug: 4.21 doesn’t load up anymore - if you disable “allow static lighting” in the project settings.
Just tested with a blank project and can confirm this is what is causing the problem. It’s stuck loading at 45% and never goes any higher.
Without that option disabled, 4.21 loads just fine.
In all versions before, I could always disable “allow static lighting” in the project settings and the editor would load up just fine in under 20 seconds (usually less than 10 seconds).
Can we please have a fix for this problem in the next quick-patch?