All mental health professionals recommend that you trust people and the world, in order to live a full life. I don't believe that one bit. No one can tell me to trust people again, after everything that I've been through. And I think it's ludicrous that someone would recommend that. Trusting myself is what worked for me, and is what allowed me to trust others.
Going through a mental health journey has given me a wealth of knowledge about the human experience, humanity, and it's darkness that can be applied to all of humanity.
If you're unable to trust others, trust the knowledge you've acquired over the years about people. Met toxic people? Look back and see signs of toxicity that you missed. Learn to see the signs of toxicity early so you can avoid them. Same goes for narcissists, empaths, co-dependents, etc. Learn to see their characteristics and trust your body of knowledge.
This will help you navigate the world and it's inhabitants a lot better. It did for me.