My opinion: Never draw attention to negatives.
You may well never have mental health issues again. Hopefully not. Telling them about your mental health issues doesn’t enhance your application, IMO. Mental health issues have a sneaky way of coming back, and they are aware of this.
Every student suffered due to the pandemic. Many struggled to get back on track for a couple of years after the pandemic, and many still struggle. The things you are saying sound like excuses, IMO.
If the school you are applying to is very competitive, there will be many other students who suffered mental health issues but managed to stay on top of their grades. Hopefully the admissions officers will look at your app for its strong points. Your recommendations will probably be important. If you think you need to explain a C, you’re mistaken. A D or F might require explanation. Not a C, especially not a C in art.