RT is going to be broadcasting propaganda , but we have to remember that so is the BBC, Fox news & pretty much every single other channel.
You can trust each news outlet to report the worse of each nation (with a bias edge), some of the things you see in RT will not get shown on the air in the rest of the west - but on the flip side - RT refuses to report criticisms of Putin or the suppression of free speech (so you can only view that side from other news outlets).
RT is motivated to expose failings of the US, if they are also true then it's a much better story - if 9/11 is an inside job or not isn't really something I'm qualified personally to have an opinion on .
All I can say is that the USA has historically engaged in false flag operations & some parts of the government/private sector had a motivation.
It's not outside of the realms of possibility but the chances of finding clear evidence either way seem remote, even if somebody found something which seemed damning it would be disregarded instantly as being conspiracy theories nonsense.
From a political perspective it would be interesting if RT released a warning saying that the USA will perform a large terrorist act on the west over the coming months to justify a war via the usual proxy terrorists (through Saudi Arabia), if it's not true then nothing is lost.
If it is true then it renders a potential strategy of the US to get involved void.