Valve have expanded Counter-Strike: Global Offensive's anti-cheat tech with new restrictions blocking third-party software which interacts with the game. 'Trusted mode' cuts off certain types of cheat, which is good. It also has the side-effect of blocking popular legitimate software including Nvidia Freestyle graphics filters and certain modes in OBS, the video capture & streaming tool. That's it working as intended but also, y'know, a bummer. Some people are reporting performance problems too.
"CS:GO now significantly restricts the types of programs and files that can interact with the game," Valve explain. "By default, players will launch CS:GO in Trusted mode, which will block third-party files from interacting with the game." That means if software it disapproves of is loaded, you'll get an error mode and be prompted to restart the game in Trusted with the files blocked. See the Trusted mode FAQ for more.
You can use a command line option to launch the game in untrusted mode, but you won't be able to play on VAC-secured servers and Valve note this will negatively affect your trust score. That's the complex metric they use to judge how legit a player is, and folks with lower trust scores can get placed into matchmaking queues with other less-trusted people - who are more likely to be cheats or wrong'uns.
Some third-party tools will still be able to work with CS:GO if they have signed .dlls, but some seem straight-up blocked. The makers of OBS explain on Twitter that this blocks the software's Game Capture mode, so "Players will need to use Window Capture with non-fullscreen modes or use the --untrusted launch option if you must play in fullscreen." That's not ideal. Some players are also finding they can't get the game to launch in Trusted mode, and it won't tell them why.
Trusted mode isn't meant to be a panacea for all CS's cheating problems; it's just another tool in Valve's anti-cheat arsenal. Reportedly some cheatmakers have already bypassed it, which, yeah, that sounds like the endless anti-cheat arms race to me.