i have found out that if i run synaptic as regular user from terminal, it works. but xfce synaptic menu item opens password dialog at first. i would like it opens password dialog only when it is needed, for example when going to install, or, that there are 2 synaptics in menu. debian 10.
Not enough info on your point? Synaptic is not an xfce program. Double menu entries is not standard debian. 'synaptic' alone should not be in the users path. At this point authority is serviced by pkexec, and can be passwordless if you'd like. I believe is does use root to secure and lock the apt database. An alias or other trick seems to be in use here.
This is not an Xfce bug.