The law of war manual is quite clearly what we should be following

How so? on what basis?

In what sense can the government of Biden be understood to be ruling under martial law (which is what belligerent occupation is)?

11.1.1.1

The conduct of military occupation has also been characterized as an exercise of “military government” or “martial law.”

....

This manual uses the terms “military occupation,” “belligerent occupation,” and “occupation” to refer to situations governed by the law of belligerent occupation.

The law of war manual is quite clearly what we should be following

How so? on what basis?

How can the government of Biden be understood to be ruoling under martial law (which is what belligerent occupation is)

11.1.1.1

The conduct of military occupation has also been characterized as an exercise of “military government” or “martial law.”

....

This manual uses the terms “military occupation,” “belligerent occupation,” and “occupation” to refer to situations governed by the law of belligerent occupation.