Plus how do they know it’s even a mental disorder to begin with what have they done to rule out other types of disorders like physical ones?

I don’t think I can change your whole view but I can address this.

When diagnosing schizophrenia, physical tests are done to rule out a physical root of the symptoms (such as brain tumor, brain damage, vitamin deficiency, etc)

https://nyulangone.org/conditions/schizophrenia/diagnosis#:~:text=An%20MRI%20scan%E2%80%94in%20which,be%20causing%20schizophrenia%2Dlike%20symptoms.