HDMI-1 not connecting to monitor after update to 20.04 LTS

Question

Before the update from 18.04 to 20.04, I could connect to my old HANNS-G HSG1078 monitor with HDMI, now all connection is lost! The monitor still works fine with other computers.

Below all the background info I could find:

First, the result from xrandr -q --verbose:

HDMI-1 disconnected (normal left inverted right x axis y axis)
Identifier: 0x43
Timestamp:  787662
Subpixel:   unknown
Clones:    
CRTCs:      0 1 2
Transform:  1.000000 0.000000 0.000000
            0.000000 1.000000 0.000000
            0.000000 0.000000 1.000000
           filter: 
HDCP Content Type: HDCP Type0 
    supported: HDCP Type0, HDCP Type1
Content Protection: Undesired 
    supported: Undesired, Desired, Enabled
max bpc: 12 
    range: (8, 12)
content type: No Data 
    supported: No Data, Graphics, Photo, Cinema, Game
Colorspace: Default 
    supported: Default, SMPTE_170M_YCC, BT709_YCC, XVYCC_601, XVYCC_709, SYCC_601, opYCC_601, opRGB, BT2020_CYCC, BT2020_RGB, BT2020_YCC, DCI-P3_RGB_D65, DCI-P3_RGB_Theater
aspect ratio: Automatic 
    supported: Automatic, 4:3, 16:9
Broadcast RGB: Automatic 
    supported: Automatic, Full, Limited 16:235
audio: auto 
    supported: force-dvi, off, auto, on
link-status: Good 
    supported: Good, Bad
CONNECTOR_ID: 92 
    supported: 92
non-desktop: 0 
    range: (0, 1)

And lspci | grep VGA gives:

00:02.0 VGA compatible controller: Intel Corporation HD Graphics 620 (rev 02)
00:1f.5 Non-VGA unclassified device: Intel Corporation Device 9d24 (rev 21)

There seems to be 2 kernel drivers in use:

 lspci -nnk | grep -i vga -A3 | grep 'in use'
 Kernel driver in use: i915
 Kernel driver in use: ath9k

I tried specifying the resolution, using values from the HANNS-G manual (https://manualsbrain.com/en/manuals/1288455/?page=14) like so:

xrandr --addmode HDMI-1 "1680x1050"

But it still doesn't connect. Hoping that someone here can see what might be wrong.

Answer 1

Finally managed to restore the connection! Basically following these steps:

https://unix.stackexchange.com/questions/227876/how-to-set-custom-resolution-using-xrandr-when-the-resolution-is-not-available-i

gtf 1920 1080 60

# 1920x1080 @ 60.00 Hz (GTF) hsync: 67.08 kHz; pclk: 172.80 MHz
Modeline "1920x1080_60.00" 172.80 1920 2040 2248 2576 1080 1081 1084 1118 -HSync +Vsync

xrandr --newmode "1920x1080_60.00" 172.80 1920 2040 2248 2576 1080 1081 1084 1118 -HSync +Vsync
xrandr --addmode HDMI-1 "1920x1080_60.00"
xrandr --output HDMI-1 --mode "1920x1080_60.00"