Following @alecxs advice, I managed to exit loop and enter download/odin mode:
1) Just drain the battery until it turns off.
2) Hold vol+ and vol- while connecting usb cable.
3) Press vol+ to enter download/odin mode.
ps. The fix of the system is subject of another question.
The data of the power supply indicates that it is compliant with the USB Power Delivery Standard (USB-PD). If it has an USB logo there should be some sort of "power flash" within that logo to indicate that it supports USB-PD.
The USB Power Delivery standard defines backward compatibility, this means that by default the charger will output 5V and only ...
UPDATE: there are apps for isolating environment and e.g. hiding other apps. Check Island.
Unfortunately, lots of Android capabilities are limited by producers - that's the case, too. According to this link on Reddit, people are searching, but with no success. The only devices are tablets, described e.g. here on Samsung Support page for Galaxy Tab S.