Our company does the same. We are not allowed to use whatsapp for any work-related stuff. This is for several reasons, mostly security and data-loss prevention

Our company does the same. We are not allowed to use whatsapp for any work-related stuff. This is for several reasons, mostly security and data-loss prevention. On Teams we can monitor with purview what happens with personal (customer!) data, which is mandatory here in europe under GDPR. We must take steps to ensure it is only processed by entities we have a data processing agreement with. But we don't block people from using it for personal purposes of course. Whatsapp groups between colleagues to coordinate lunch options and nights out are super commonplace and perfectly fine. Even on work hardware (on android on the personal side of the phone, on iOS we just block copy/paste into whatsapp from corporate app). I even saw our CISO using whatsapp web on his corp laptop. It's fine as long as it's not used for actual work. Here in EU it is mandatory to permit some level of personal activity even on work devices.