on NixOS we have not acces to root (not to GUI only) without 'xhost' to clean system as root this package have to permanently installed.
not possible is set acces to root and remove 'xhost'. after giving acces and remove 'xhost' access is removed.
to run program (not only GUI) we must do 'xhost si:localuser:root' but after 'xhost -si:localuser:root' this acces is exists how long is installed 'xhost'
answer of terminal after 'xhost -si:localuser:root' is:

localuser:root being removed from access control list
X Error of failed request: BadValue (integer parameter out of range for operation)
Major opcode of failed request: 109 (X_ChangeHosts)
Value in failed request: 0xd
Serial number of failed request: 7
Current serial number in output stream: 9

but is the same when we want to give privilages:

localuser:root being added to access control list
X Error of failed request: BadValue (integer parameter out of range for operation)
Major opcode of failed request: 109 (X_ChangeHosts)
Value in failed request: 0xd
Serial number of failed request: 7
Current serial number in output stream: 9

and everything is working but we cannot remove this root acces without removing 'xhost' package, as second this acces is not for GUI but for cleaning as root
'sudo xhost -si:localuser:root' is not giving results
on nixos 'bleachbit' package is outdated.