Results:
volumio@zzzvolumio:~$ ls -al /dev/fb*
crw-rw---- 1 root video 29, 0 Mar 13 18:43 /dev/fb0
volumio@zzzvolumio:~$
=================================================================
volumio@zzzvolumio:~$ ls -al /usr/share/X11/xorg.conf.d
total 18
drwxr-xr-x 2 root root 1024 Mar 13 18:43 .
drwxr-xr-x 1 root root 1024 Mar 13 18:35 âŚ
-rw-râr-- 1 root root 92 Feb 7 2019 10-amdgpu.conf
-rw-râr-- 1 root root 1099 Aug 23 2018 10-evdev.conf
-rw-râr-- 1 root root 1350 Jan 4 10:05 10-quirks.conf
-rw-râr-- 1 root root 92 Apr 6 2019 10-radeon.conf
-rw-râr-- 1 root root 1429 Mar 31 2019 40-libinput.conf
-rw-râr-- 1 root root 1099 Mar 13 18:43 45-evdev.conf
-rw-râr-- 1 root root 2747 Jun 26 2017 70-wacom.conf
-rw-râr-- 1 root root 607 Mar 13 18:42 99-fbturbo.conf
volumio@zzzvolumio:~$
=================================================================
volumio@zzzvolumio:~$ cat /boot/config.txt
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
force_eeprom_read=0
include userconfig.txt
volumio@zzzvolumio:~$
=================================================================
volumio@zzzvolumio:~$ cat /boot/userconfig.txt
Add your custom config.txt options to this file, which will be preserved during updates
dtparam=spi=on
dtoverlay=mhs35
volumio@zzzvolumio:~$
=================================================================
After installing the plugin the HDMI display presented the Volumio UI soon after prompting for user/password.
After executing the set of commands the HDMI screen did not show the Volumio UI after the user/password prompt (it remained dark).
as mentioned above: no login prompt on LCD screen (only on HDMI)
LCD screen remains white (with no change)
Toggling the plugin makes no change
Error connecting to xserver , keeps popping up
When trying to update plugin setting of mouse pointer I get the message:
Touch Display
Error applying pointer settings: Error: ENOENT: no such file or directory, stat â/tmp/.X11-unix/X0â
BTW. the 3.5 LCD display was working OK under Raspberry OS (set of commands received with the display). When I did try before to install under volumio (other threads) it did turn black but no display and it seem to respond to touching it (the mouse pointer had moved on the HDMI screen).