AssetBundles must be built with the AbBuilder tool instead of Unity's AssetBundle Browser since the resulting AssetBundle must be patched to set the platform to Switch and replace some references.

Preparations

Assign the AssetBundle in the asset's inspector as usual (some import tools do this automatically)

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Build

Open the AbBuilder tool in Tools/AbBuilder and enter the path where the AssetBundles should be built (e.g. ../build/romfs/Data/StreamingAssets/ab/.) Expand Bundles to configure which AssetBundles should be built and click Build to start the build. The Option Skip Postprocessing should only be checked for debugging purposes.