OK, that makes sense. At around revision 364, nVidia enabled support for kernel modesetting, but in true nVidia style, they didn't use a lot of the kernel infrastructure but rolled their own. Among the problems are lack of support for the fbdev high resolution framebuffer.
What this means for you is that at the moment, you're not making use at all of kernel modesetting, but instead late modesetting, by which time X is starting and negotiating its own screen mode. It's then able to settle on a 4K resolution.
The steps I'd like to go through to test that this is really the case are:
1. Dump and extract the EDID your system is currently using. This will allow me to confirm whether it's the Denon's EDID or the screen's.
2. Upgrade your nVidia driver - you may end up with a few days on 1920x1080 as we're on different timezones while we go through this. Don't panic!
3. At that point, I'll need to see things like your xorg.log and some output from xrandr etc. to see what your computer thinks is connected to it.
4. We'll check boot options, initially disabling modesetting to force the nvidia module to use the old method of negotiating a screen (though this will slow down your boot time, which is important to you for some reason
)
5. If that's not satisfactory, we'll force the system to use the EDID that we extracted in Step 1.
Reasonable? If so, then first instruction is:
sudo apt-get install read-edid
daniel@daniel-System-Product-Name:~$ sudo apt-get install read-edid
[sudo] password for daniel:
Reading package lists... Done
Building dependency tree
Reading state information... Done
The following packages were automatically installed and are no longer required:
linux-headers-4.15.0-43 linux-headers-4.15.0-43-generic
linux-headers-4.15.0-45 linux-headers-4.15.0-45-generic
linux-headers-4.15.0-46 linux-headers-4.15.0-46-generic
linux-headers-4.15.0-47 linux-headers-4.15.0-47-generic
linux-headers-4.15.0-48 linux-headers-4.15.0-48-generic
linux-headers-4.15.0-50 linux-headers-4.15.0-50-generic
linux-headers-4.15.0-51 linux-headers-4.15.0-51-generic
linux-image-4.15.0-43-generic linux-image-4.15.0-45-generic
linux-image-4.15.0-46-generic linux-image-4.15.0-47-generic
linux-image-4.15.0-48-generic linux-image-4.15.0-50-generic
linux-image-4.15.0-51-generic linux-modules-4.15.0-43-generic
linux-modules-4.15.0-45-generic linux-modules-4.15.0-46-generic
linux-modules-4.15.0-47-generic linux-modules-4.15.0-48-generic
linux-modules-4.15.0-50-generic linux-modules-4.15.0-51-generic
Use 'sudo apt autoremove' to remove them.
The following additional packages will be installed:
libx86-1
The following NEW packages will be installed:
libx86-1 read-edid
0 upgraded, 2 newly installed, 0 to remove and 0 not upgraded.
Need to get 94.1 kB of archives.
After this operation, 336 kB of additional disk space will be used.
Do you want to continue? [Y/n] y
Get:1
http://la-mirrors.evowise.com/ubuntu bionic/universe amd64 libx86-1 amd64 1.1+ds1-10.2 [75.2 kB]
Get:2
http://la-mirrors.evowise.com/ubuntu bionic/universe amd64 read-edid amd64 3.0.2-1build1 [18.9 kB]
Fetched 94.1 kB in 1s (68.1 kB/s)
Selecting previously unselected package libx86-1:amd64.
(Reading database ... 540208 files and directories currently installed.)
Preparing to unpack .../libx86-1_1.1+ds1-10.2_amd64.deb ...
Unpacking libx86-1:amd64 (1.1+ds1-10.2) ...
Selecting previously unselected package read-edid.
Preparing to unpack .../read-edid_3.0.2-1build1_amd64.deb ...
Unpacking read-edid (3.0.2-1build1) ...
Setting up libx86-1:amd64 (1.1+ds1-10.2) ...
Processing triggers for libc-bin (2.27-3ubuntu1) ...
Processing triggers for man-db (2.8.3-2ubuntu0.1) ...
Setting up read-edid (3.0.2-1build1) ...
daniel@daniel-System-Product-Name:~$
I completed a back up before starting on this...So feel free to play fast and loose with this.":O}
Many thanks K. I always knew you were one of the good ones. I would have told you but wished to spare you vanity.":O}