Dell Inspiron 17 3000 Series 3785 problem with X

[ernst doubt <ernstdoubt25@gmail.com>]

Hi all,

i had sent a message to debian-laptop a few hours back, but all i've
seen so far is one response (suggesting i use q4os). i'm pretty
committed to using debian directly though (at least until i've tried an
awful lot more things).

After installing buster, this brand new laptop of mine seems to hang on
X (GDM) starting -- after briefly showing a flashing underscore char in
the top left corner of the screen, it drops back to command-line output
(but doesn't allow me to login).

i'm booted into recovery mode right now and i've managed to get
networking up and running (and installed emacs-nox and gpm, yay!) and
i'm looking through /var/log/daemon.log from my failed boot last night.

My assumption is that there's probably some non-free firmware package i
need to install (and maybe configure?)

20 years ago or so i remember fighting with modelines entries in order
to get X working, but i imagine things have changed.

This machine purportedly has:
AMD Ryzen™ 5 2500U Mobile Processor with Radeon™ Vega 8 Graphics

If anyone has any suggestions or hints about how to proceed with
troubleshooting, i'm happy to share log files, chase down
documentation, install packages, edit configuration files or whatever
else is needed. i could also burn an ubuntu disk and boot that live to
see what i could learn from that experience (a web search seems to
indicate ubuntu would install fine on this laptop, but my preference is
to stick with debian).

    thanks so much in advance,
        ~e