Any resolution from the UN has to get approval from the security council iirc so if the US or UK object it'll never be formally adopted by the UN.

> They mention legal concerns from Washington but don’t explain them for some reason.

Odds are they haven't actually been spelled out because they amount to "it'll cause huge disruptions to business because they'll all suddenly be suable for their decades of environmental damages". The government is maximally vague on these things so it's harder to actually refute.