UN is toothless without the US. Alas, US populace is tired of being chastised for spending massively and making mistakes on Pax Americana[0]. So, the US will increasingly isolate and won’t have the will to stand up to Russia and China aggression, which they are aware of and increasingly taking advantage of in the last decade. UK, France, and India aren’t formidable; not that they’d be willing. As you wish, we’ll find out how effective the UN’s deterrence is in the next decade.

[0] https://en.m.wikipedia.org/wiki/Pax_Americana