On some blogs in the internet it was suggested that the upgrade from Debian 10 to 11 is very easy. No it isn't. First problem is to fix the /etc/apt/sources.list file. There are different tutorials how to do so. Theuser has to change the name of distribution, but also the URL to the security mirror server. But suppose the user has carefully recreated the file and has run the “apt upgrade” command. What he can expect then is that only the kernel was updated. After rebooting the machine important programs like the e-mail software evolution or the matplot library doesn't work anymore. But at least the gnome environment seems to be stable. So the user will run for sure the apt full-upgrade command but this will make things worse. After the next reboot the icons on the desktop are missing and it is not even possible to start the terminal program. That means a simple attempt to upgrade the operating system has caused a system wide failure.
Only after manual login into a text only session next to the gnome X11 session and updating the system again will solve the issue. After many reboots, autoremove commands and fixing lots of minor problems it is some sort of miracle that the gnome session is running normal. That means the new Debian 11 system is booting and at least major programs like the Terminal and the Firefox browser can be started.
What we can say for sure is that the upgrade to debian 11 is working with lots of trouble and it is compared to Windows 10 not recommneded for beginner computer users. Linux (especially Debian) remains a construction site and the chance is high that after rebooting the machine the user can't login anymore.