I started seeing that, too, a couple of weeks ago. On a computer, you would see that first, enter your password, or choose a different user, before proceeding. Since there is only one user on the L5, I imagine this was set to just advance to the password screen automatically, but was previously hidden from view. No biggie.
I’ve been seeing that login screen flash for a few seconds during startup since the beginning, with the default “Librem5” user (I haven’t changed my username yet). I just assumed it was a loose end legacy from desktop that hadn’t been tidied-up yet. Are you all saying that you’ve just started seeing this now?
It appeared for me after installing some app like librem5-goodies (on Amber no problem, but on Byzantium yes). I had to reflash my l5 to fix it. I had the impression that the boot took longer, but maybe I was wrong.
That’s gdm, GNOME’s login manager, a beautiful piece of free software. You must have installed it as a dependency of some other application (likely that app depended on something that then in turn depended on something that then depended on gdm - the wonders of Debian… err… PureOS).
If you want to uninstall/investigate why it was installed, open the terminal app and run
sudo apt remove gdm3
and it will likely tell you, which software packages require gdm to be installed.
This was discussed in very related earlier thread: Byzantium configuration, therefore finding it helpful. Also apt info gdm3 will show you clearly on why this package is not recommended on Librem 5. Just type: Yes (after: sudo apt purge gdm3), don’t close your eyes and hit Enter key (now you may close your eyes). Followed by: sudo apt autoremove, type: Yes, don’t close your eyes (not yet) and hit Enter key.
So, I removed gdm3 also, and it fixed my startup process (no desktop splash screen). Interestingly, when I sudo apt removed it, it didn’t reveal any dependencies, so it was probably installed for something I had installed and subsequently removed very early in having my phone. I can’t for the life of me think what that might have been, though.