NewInBuster - Debian Wiki
The su command in buster is provided by the util-linux source package, instead of the shadow source package, and no longer alters the PATH variable by default. This means that after doing su, your PATH may not contain directories like /sbin, and many system administration commands will fail. There are several workarounds:
Use su - instead; this launches a login shell, which forces PATH to be changed, but also changes everything else including the working directory.
Use sudo instead. sudo still runs commands with an altered PATH variable.
To get a regular root shell with the correct PATH, you may use sudo -s.
To get a login shell as root (equivalent to su -), you may use sudo -i.
Put ALWAYS_SET_PATH yes in /etc/login.defs to get an approximation of the old behavior.
Put the system administration directories (/sbin, /usr/sbin, /usr/local/sbin) in your regular account's PATH (see EnvironmentVariables for help with this).
The default Wayland session for GNOME stops some packages like synaptic from working. Graphical system administration packages that need superuser privileges will generally be problematic until major rewrites occur. Workarounds include using GNOME on X11 instead of Wayland, or using non-graphical alternative tools.
The security settings for some components of systemd have been tightened. People using nis with systemd may encounter bug 878625 which breaks a variety of things related to login sessions. Workarounds include installing the nscd package, or reconfiguring systemd-logind.service to allow it to use the network.