No deck list on startup; "study deck" does not display cards; etc

Anki on my laptop is displaying a number of problems. On startup I see no list of decks, no way to browse, etc.:

If I do Tools → Study Deck I get exactly the same screen:

If I make my way to the browser (in this case by using “check media” to find some bad LaTeX) I can see the list of cards, but no way to edit:

This behavior persists if I hold shift as I start, and persists across versions: I’ve tried 2.1.44, 2.1.49, 2.1.54qt5, and 2.1.54qt6.

On startup I see

nargothrond:software$ ./anki-2.1.54-linux-qt5/anki 
Anki starting...
Initial setup...

Preparing to run...
Command 'dbus-send --session --print-reply=literal --reply-timeout=1000 --dest=org.freedesktop.portal.Desktop /org/freedesktop/portal/desktop org.freedesktop.portal.Settings.Read string:'org.freedesktop.appearance' string:'color-scheme'' returned non-zero exit status 1.
Starting main loop...
mpv not found, reverting to mplayer
conf key imgocc should be fetched with col.get_config(), and saved with col.set_config()
conf key imgocc should be fetched with col.get_config(), and saved with col.set_config()
conf key imgocc should be fetched with col.get_config(), and saved with col.set_config()

I’m on Debian Bullseye.

I’m at my wits’ end—does anybody have any idea what’s going on here? How can I get more debugging information?

Do you have a proxy, a VPN, or have (mis)configured your firewall? All these can block Anki’s rendering.

None of the above. (At least not this instant—I haven’t used my work VPN in a week or so, and it didn’t cause trouble then.) A couple of relevant lines from lsof -i tcp:

anki      3042 christopher   14u  IPv4  29568      0t0  TCP localhost:35535 (LISTEN)
anki      3042 christopher   42u  IPv4  24258      0t0  TCP localhost:8765 (LISTEN)

FWIW tcpdump -i lo shows packets going through when I muck about in the Anki UI, but I don’t really know what I’m looking for.

Are you sure you tested the Qt6 version? Blank Main Window - Anki Manual

I’m 98% sure I had, with the same poor results.

But retesting now, the qt6 version works! Thank you!