That sounds good in theory, but what is the standard of checking the proofs?

The same way as it is done on the judges: keep silence, and let all parties say their agruments, without pressure, interruptions, muting etc. And then, try to evaluate them, find lies or untold things etc.

Actually, there was an attempt to make such an open discussion in UN Security Council, but it was banned by GB.

Also since Russia uses lying as a primary political tool, how can we trust anything they say?

Exactly the same I can tell about West? I'm Belarusian, and I'm an eyewitness of August 2020 events in my country, and I know how the events were highlighted in western media. If there is no open discussions, ane everybody just attributes to oppenents as "liars", that actually means, that parties are not interested in listening to others, and find some kind of truth.