Minecraft 1.20.1, Forge 47.3.0, any mod version ≥2.0.0.

Placing blocks with the arrow indicator on the ground places blocks that have normally shaded faces, placing blocks with the arrow facing upwards causes broken shading. Rolled back to 1.8.0, works perfectly fine.

This is most likely a conflict between a mod that modifies block rendering, and the rotated models feature introduced in 2.0.0. either find and remove the offending mod, or disable rotated models in the client config.