Does corporate data leak uncontrolled to personal devices when users employ native Talk app? (GDPR)

Dear all,

for the public sector Nextcloud is interesting to follow up on their security and data protection requirements.

Let’s assume now a public organisation uses Nextcloud and individual staff members find out about the Android/iOS native apps to join calls and chats. They install the apps on their personal (non-corporate) phone and start chatting.

I am concerned that this way, corporate confidental messages could leak uncontrolled to the staff personal devices. I clicked on the privacy notice in the menu and got forwarded to

Unfortunately, I could not find out whether the Android mobile app retains chat messages or other data on the phone and if so, how it is protected.

Do you know how secure such corporate information from the Nextcloud is when transferred to personal devices via the Nextcloud Talk app on Android/iOS?