The doc is outdated. There is also an issue with the way the autologin block gets populated.
Manually editing the kde_settings.conf file is the only way to get it to work
[Autologin]
Relogin=false
Session=plasma.desktop
User=radxa
Note the plasma.desktop session. If you use the GUI that option is set to plasma and this doesn't work.
The doc is outdated. There is also an issue with the way the autologin block gets populated.
Manually editing the kde_settings.conf file is the only way to get it to work
[Autologin]
Relogin=false
Session=plasma.desktop
User=radxa
Note the plasma.desktop session. If you use the GUI that option is set to plasma and this doesn't work.