Hello,
On Vision OS we do not currently support shaders in asset bundles because shaders in VisionOS must be represented as MaterialX rather than compiled shader bytecode.
You can reference shaders that come packaged in your game build from an asset bundle. We have logged your interest but also recommend that you submit an idea here: https://portal.productboard.com/unity/77-unity-visionos-roadmap/tabs/272-mr-immersive-features as a feature request on the roadmap so others can vote for it.