Thierry de Coulon wrote:

> Just decided to let my Debian 10 update, which it did. Next reboot I got
> greeted by xfce's login screen (I had installed Debian with xfce), managed
> to find my way back into TDE running the usuall dpkg-reconfigure lightdm.
> 
> However I was wondering: if I remove lightdm, what will happen next
> update?

Looks like last installed is last configured. If you remove it it should
stay with TDM. It is basically changing links in the background that point
to the one that is assumed as default or selected AFAIR.