I also have this problem where suddenly in 2021 LTS progress bar shows 125M shader variants and build time increased dramatically beyond reasonable usability.
URP, Android Vulkan backend. No decals, no screenspace shadows. Mobile SSAO. 5 quality presets. Addressables in project. Few scenes with different lighting settings. It was fine on 2021.1, it is ~10 times slower on 2021 LTS.
Supposedly there’s a fix coming in this area (see: Build time taking almost a day - URP page-2#post-8107979) but it’s hard to tell if it’s an acknowledgement of the problem we share because there’s a bit of a “you’re holding it wrong” vibe in next posts.
IDK, maybe we are “holding it wrong”, hopefully someone figures out what triggers the 10-fold slowdown of 2021 LTS.