Hi
you have an xorg.conf please attach it.
Is 18.3.....the new usb system rock stable? any glitches?
and it looks like you may be using uxa
Option "AccelMethod" "uxa"
and because you have no 20-intel file.....me thinks you have it in your xorg.conf
However....you have succeeded....on 18.3 where I failed to get your 19 to have intel as the driver
which is a big ticket, with 1680x1050
disappointment is your grub2 veinfo said you could get 1920.....aaah well this is a good start.
do not over write your original mx 18 usb stick that you used.....to create this one please.
I am tempted to see if we can do an upgrade instead of a clean install.
but unfortunately I still want to see your xorg.conf......and where did you get it from please?
below are a few modelines we may look later.....to compare on 19
Modeline "1680x1050"x0.0 146.25 1680 1960 2136 2240 1050 1053 1059 1089 -hsync +vsync (65.3 kHz eP)
Modeline "1280x1024"x0.0 135.00 1280 1296 1440 1688 1024 1025 1028 1066 +hsync +vsync (80.0 kHz e)
Modeline "1280x1024"x0.0 108.00 1280 1328 1440 1688 1024 1025 1028 1066 +hsync +vsync (64.0 kHz e)
Modeline "1600x1200"x0.0 162.00 1600 1664 1856 2160 1200 1201 1204 1250 +hsync +vsync (75.0 kHz e)
EDIT
I wonder if the updated mesa/oxrg on 19 is the issue for your specific video...........most people seem to be OK including me
18=libegl1-mesa:amd64 18.2.6-1~mx17+1 .......my 19=libgl1-mesa-dri:amd64 18.3.6-2
18=X.Org 1.19.2.......................................my 19 =1.20.4