Thanks for the quick reply, this is my first experience
with the debian-user mailing list and it makes for a positive
one.
I ran nvidia-detect every now and then and it doesn't tell
me exactly which version to install. Instead, it tells me that
my card is "OK" (not legacy, GTX-1070 Ti) and that I should
simply go and install nvidia-driver. I did that both times,
once running from the standard debian repo, which installs
version 418, and once also from debian-backports, which
installs version 450 (both is OK per Debian wiki
here). Previously this worked
fine, but now those processes fail me as well, so something is
different this time, I just don't know what.