We are buying a 40 year old house with this breaker panel on the inside, but there is no door or any markings I can see identifying the brand of the panel. The main 200amp breaker seems fairly unique to me, so hoping that can help narrow it down.
The older breakers with their beveled handles, and in particular the rounded-over main breaker case, is the distinctive design language of Murray panels.
It doesn't really work to look at 1 breaker in a panel and guess what panel it is, because people put the wrong breakers in panels all the time (and that is dangerous).
However, when ALL the older breakers speak one particular design language, it's a sure bet that's the panel type.
Murray is a perfectly common and current panel type, and it takes Siemens MP breakers (which Siemens has oddly renamed to QP for no good reason). Siemens MP/QP breakers are fine.