Wrong resolution on 7" screen

I have seen this question by numerous CB1 users and not a single answer from BTT.
I have Waveshare 7" touchscreen. In leaflet that came with the screen is written:
Append the following lines to config.txt:
hdmi_group=2
hdmi_mode=1
hdmi_mode=87
hdmi_cvt 1024 600 60 6 0 0 0

Also, in CB1 install settings is this:
CB1 will automatically identify the HDMI resolution, but if your HDMI screen cannot report the resolution through the EDID normally, we can forcibly specify the resolution of CB1 output by uncomment extraargs=video and set the actual resolution.
For example:
BTT-HDMI7 resolution = 1024x600: extraargs=video=HDMI-A-1:1024x600-24@60

Nothing of that doesn't work. No matter what I do, I have the same result. Bottom of the screen is missing by approx 200 pixels.

Screen is not listed in xrandr output. Is there no driver installed at all?

Start by reviewing the CB1 install settings for extraargs=video and the display configuration in config.txt, then compare the reported output with the Waveshare 7" requirements. Use xrandr to check whether the HDMI display and 1024x600 mode are detected. Done means the full 1024x600 screen is visible and the resolution is reported correctly.

Written by the indexing model from the issue text.