Which Android OS version is supported ?

You need at least Android 9 or higher. 

The Android phone should have a google playstore installed. 

Will there be Android 6-7 support?

Since Android 6-7 has only about 2% market share, more likely no. 

Will there be an APK/APKM for manual installation for Huawei/Xiaomi users?

Currently No. But not excluded at a later date. 

We are currently still checking the demand.

If possible, do not download APK/APKM from Internet sources, as they may contain malware.

Delete all CLINQ user data (login/name/email/call lists)

In CLINQ Desktop (Win/Mac/Linux) log in->Settings->Profile->"delete account

When deleting is finished, you will be logged out and can then uninstall CLINQ or create a new CLINQ profile. 

The deletion of the CLINQ profile via CLINQ Android will come later.