From reading through your lightdm.log, it looks like you are trying to start Xfce as a wayland session (not xorg).
Probably not a good idea.
Xfce is not ready for that, as far as I know.
I never tried …
In theory the latest update kind of supports it, like a first alpha…it maybe sometimes works but i would not do it to myself on my daily driver machine.
Important Notice: Please be aware that the Wayland support in Xfce 4.20 is experimental. It is recommended for advanced users only, as you may encounter bugs and experience incomplete functionality. Proceed with caution!
So far Xfce does not feature a compositor which supports Wayland. If you want to run Xfce in Wayland, Labwc and Wayfire will give you the best results. A detailed instruction on this can be found here. Please be aware that Wayland support is still experimental!
Plans are underway to add Wayland support to Xfwm4 while preserving its existing X11 functionality. However, such a restructurization will be a major effort and we cannot tell yet when/if it will be done, so please don’t hold your breath waiting for it.
For few components and multiple features, it was not possible to port them to Wayland, partly because there are no standardized Wayland protocols available yet to provide the required services
Some other Xfce components don’t run at all on Wayland:
More detailed info on the current Wayland status can be found on our Wayland roadmap.
On the lightdm login screen, as in other display managers, you can select / choose between a Xfce session and a Xfce Wayland session.
Maybe you chose inadvertently - by mistake, did not even notice.
It’s just a click away to change the check mark from one to the other.
With the default configuration of lightdm, there is a kind of panel at the bottom of the screen with some icons/options on the right side - poweroff is one of them
Another one lets you select and switch between xorg and wayland.
But as I understood it, you changed your greeter - so I don’t know where that option would now be for you.
Proof of everything still working is that you can start your session via startxfce4 - as you mentioned.
I chose Xfce Wayland weeks before because I tried every setting to get out of the loop when I first encountered it, then settled for startxfce in tty and ignored the bug for a couple of weeks until I had to reboot recently again and decided to make work of this.
So I’m guessing it had been a combination of factors (the original I must have fixed with all the things I’ve tried) that kept me in this loop.
but i would not do it to myself on my daily driver machine.