Nextcloud Android hooks data deletion prompt

I just learned, that in recent Android, apps can hook their own data deletion prompt in properties and show a custom activity.
I learned that through the Nextcloud Android App, being the first one doing that on my phone.
Aside from the sheer insanity that apps are allowed to do that,
I am particularly offended about Nextcloud as an open source “culture” app doing it.

On the technical side, if I press the button to delete in Nextclouds custom data deletion activity, the app does not actually exit and neither deletes its own data completely. The Android properties page still reports about 200kb of non-apk appdata existing.

Might someone please elaborate on why this is even implemented and how I can be assured that every trace of actual data and useless data is definitely wiped?

I admin about 24 Nextcloud instances, but don’t use it for my private things. I am not in a business relationship with you yet due to a lot of doubt for a bunch of small reasons that are OT here.
I recognized this because a user was confused about this because she is used to non hooked appdata deletion screens and it is required in her workflow.

I wish you all a nice end of the year, whatever you celebrate.

(Ist “herunter geladene” wirklich getrennt?)