Steps to Reproduce:
Import any resource pack with PBR capabilities;
Enable the experimental toggle for Render Dragon features;
Switch rendering mode to "Deferred Technical Preview";
Leave the world.
Observed Results:
The world's thumbnail is a blank skybox.
Expected Results:
The world's thumbnail renders the blocks.
Notes: This wasn't an issue before this version.
As of 1.21.10.20 Preview, the background turns completely white instead of rendering the skybox.