I don’t use “prolly” at work and don’t personally consider my coworkers casual or close friends, more like arm’s length acquaintances.
I have more a problem w/actual misspellings born of blatant ignorance. “Prolly” to me doesn’t automatically = “blatant ignorance.”
I also take the view that language is constantly evolving.
If some people don’t understand when to speak/write formally vs. when being casual is acceptable, well, that’s not on me as someone who does understand that distinction.
I wouldn’t use slang or text shorthand when sending a work-related email to a local government official I was approaching to coordinate an interview. I might use slang or text shorthand with a friend in a non-work context. If other people lack boundaries, that’s a them problem not a me or even frankly probably a societal problem. It’s a problem with how that person was raised and if it bothers you, then reply back formally and hope they take the hint.