What’s this diagonal metal strapping between my studs?
In my opinion, that should not be cut. It appears to be a structural part of the house. There will be others like that in the wall, at least 1 more, and if the wall is over 20' it will most likely have an extra one, 3 total. That was code minimum back in the day, and probably still is.

There is a chance that nothing would ever happen bad if it was cut, but that chance, I cannot recommend removing it. Code guidelines are the minimum, never advisable to do something that reduces the effectiveness of a building component that is structural in nature.