Please provide the brand and exact model name of the display.
Well, I got it from Amazon (B07YJDSCKR), but there is no specific brand. Since the images on Amazon are not correct, here is one. 
But as mentioned: I got the same result when testing with the official Raspberry Pi 7 Inch Display.
Thanks for the picture.
Please post the results of
cat /boot/config.txt
and
cat /boot/userconfig.txt
I kind of solved the problem - the description claims the display to be 16:9, but 1024x600 is 16:10, so I changed the resolution to 1024x576 et voila.
Anyway:
initramfs volumio.initrd
gpu_mem=32
max_usb_current=1
dtparam=audio=on
audio_pwm_mode=2
dtparam=i2c_arm=on
disable_splash=1
hdmi_force_hotplug=1
include userconfig.txt
Volumio i2s setting below: do not alter
dtoverlay=i-sabre-q2m
Add your custom config.txt options to this file, which will be preserved during updates
config_hdmi_boost=7
hdmi_group=2
hdmi_mode=87
hdmi_drive=1
hdmi_cvt=1024 576 60 6 0 0 0
Has the height been set intentionally to 576?
Apart from that try adding
max_framebuffer_width=1024
max_framebuffer_height=1024
framebuffer_width=1024
framebuffer_height=600
to /boot/userconfig.txt above the current lines. I would also set the height value in “hdmi_cvt” (back) to 600 for testing.
Yes, that was intentionally - see post above. I tried your settings and the display works the same as before: ellipse. Only with a genuine 16:9 resolution I can get circles
1 Like
@gvolt this is standing on amazon :
Aspect ratio 16:9
max_usb_current=1
hdmi_force_hotplug=1
config_hdmi_boost=7
hdmi_group=2
hdmi_mode=87
hdmi_drive=1
display_rotate=0
hdmi_cvt 1024 600 60 6 0 0 0
in his post we missed the max_usb_current=1
Yeah, I overlooked that 
So, do you consider the issue solved by using the height value of 576?
This value means aspect ratio 15:9. A value of 3 would be 16:9.
strange settings a 6 if you need a 3 the screen is 16:9 what i read.
seller says its a :
http://www.lcdwiki.com/7inch_HDMI_Display-C
http://www.lcdwiki.com/res/MPI7002/7inch_HDMI_Display-C_User_Manual(En).pdf
touch settings included in pdf ( libinput )
Don’t know: 1024 : 600 = 1.707 is nearer to 15 : 9 = 1.667 than to 16 : 9 = 1.778. So at first sight the aspect ratio value should be set to 6…
I think one reason why that does not really fit the display could be that the pixels of the display might not be quadratic but their height is bigger than their width.
Just out of interest: Where did you find this information?
BTW: The settings recommended in the lcdwiki are the same as the ones @bruns used.
in :
at the bottom.
Thank you.
I think so, because the overall sharpness doesn’t seem to suffer from this -on paper- wrong resolution. I now tried
hdmi_cvt 1024 600 60 3 0 0 0
but I cannot see any difference…?
… to hdmi_cvt 1024 600 60 6 0 0 0 or to hdmi_cvt 1024 576 60 6 0 0 0?
No difference between
hdmi_cvt 1024 600 60 6 0 0 0
and
hdmi_cvt 1024 600 60 3 0 0 0
sorry. But I stand corrected: I just made two photos of the screen. One -576- has the correct aspect ratio, but is noticeably more blurred.
Since I don’t have to use the screen often, I’m fine with 576. But I find it kind of odd, that even with the official screen I get an ellipse instead of a circle.
Hm, on the second photo the circle appears to be slighty elliptic, but from the photos I could not say if the first one is more blurred.
Do you still have the framebuffer settings in /boot/userconfig.txt? You might try them with
framebuffer_height=576
along with
hdmi_cvt 1024 600 60 6 0 0 0
and alternatively
hdmi_cvt 1024 576 60 6 0 0 0
Changing the frame buffer (either height or width) results in a smaller window, but since the overall resolution doesn’t change, the aspect ratio doesn’t either. I can only affect the aspect ratio by changing hdmi_cvt. But this results -naturally- in a slight blur.
I think it actually might be a problem of non squared pixels. The seller claims inner dimensions of 154.08 x 85.92mm (from Amazon) or 154.2144 x 85.92mm (the wiki). While the resolution is 16:10 (1024x600), the screen dimension is 16:9.
Is there any chance to force a different aspect ratio not related to the resolution?