One possibility is CalcService, a free utility that appears in the right-click services list. You type in a math expression somewhere (basically any app that does text editing), select it, and CalcService will solve it.
It’s in the Mac App Store and was written by DEVONTechnologies, the makers of DEVONThink.
Reverse Polish Notation. Reverse Polish notation - Wikipedia
Once you wrap your head around it, it’s almost impossible to go back. I still use my 40-year-old HP 12C when I need to resolve a string with more than one operator and two operands and don’t want to fire up PCalc or Excel.
I have an HP-35 (still working) from 1972 when it cost as I recall US$350. Also an HP-42S and the HP-12C app on the iPhone. It takes not that long to “wrap you head around it” as it’s kinda natural for computing complex precedence formula as mentioned above.
RPN is recommended to the OP to at least try.