All the “hdmi_xxx” options are irrelevant for your DSI display. In your “/boot/userconfig.txt” try replacing
lcd_rotate=2
display_hdmi_rotate=2
display_lcd_rotate=2
hdmi_group=2
hdmi_mode=87
hdmi_timings=400 0 100 10 140 1280 10 20 20 2 0 0 0 60 0 43000000 3
hdmi_blanking=1
with
dtoverlay=vc4-kms-v3d-pi4
dtoverlay=vc4-kms-dsi-7inch
P.S. Please use code tags (look for the </> symbol) when posting the output of commands that were executed from Volumio’s command prompt.