Adding another circuit to a full panel
It is okay to have 800 amps of breakers in a 200 amp service panel.  The reason there is a main breaker (200 amp double pole) is to prevent unsafe usage.

When you run out of physical space, there are several solutions:


Replace some of the main panel breakers with half-widths (two breakers per slot) to create enough space for a new breaker.





Install a sub-panel which is fed by a double breaker in the main panel.

Remove unneeded breakers.  Maybe some circuits are no longer in use.
Replace the breaker panel with a bigger one.