Install Debian Testing ( the most recent bullseye weekly build ) with KDE Plasma on bare metal

It appears that straight forward install Debian Testing via official ISO image  at least in meantime hangs . Looks like "sddm" hangs attempting to pop up logging screen prompt

First time log into in recovery mode as root ( text mode ) 

1. Make user's account (say "john") admin privileged via visudo

    either manually update /etc/sudoers as usual with "qw!"

2. # systemctl set-default multi-user.target

3. # reboot

Now perform normal logging into as "john" and issue from command prompt

$ startx 

The last command will succeed and bring up KDE, at this point we intend to fix issue with "radeon kernel modesetting" and switch back to graphical login.

1. Update /etc/default/grub setting

    GRUB_CMD_LINUX="radeon.dpm=0"

2. $ sudo grub-mkconfig -o /boot/grub/grub.cfg

Make sure you downloaded the firmware's ISO (References) 

3. $ sudo apt install firmware-amd-graphics

4. $ sudo systemctl set-default graphical.target

5. $ sudo reboot

References

1. http://cdimage.debian.org/cdimage/unofficial/non-free/cd-including-firmware/weekly-builds/amd64/iso-dvd/