Hello Vpeter,
I put the kernel you sent me on CoreELEC-Amlogic-ng.arm-9.2-nightly_20210313-Generic image. Unfortunately, the touchscreen is still dead. 
I tried to compare it to the last libreelec version where everything works fine. In my opinion, the problem is caused by the dwav_usb_mt driver which overlaps with the touch support. Take a look please:
Coreelec:
[ 4.158785@2] input: WaveShare WS170120 as /devices/platform/ff500000.dwc3/xhci-hcd.0.auto/usb1/1-1/1-1.2/1-1.2:1.0/input/input4
[ 4.159358@1] **dwav_usb_mt 1-1.2:1.0: ODROID VU7 MultiTouch(800x480)**
[ 4.159439@1] usbcore: registered new interface driver dwav_usb_mt
Libreelec:
[ 5.934141@3] input: WaveShare WS170120 as /devices/c9000000.dwc3/xhci-hcd.0.auto/usb1/1-1/1-1.4/1-1.4:1.0/0003:0EEF:0005.0001/input/input2
[ 5.934598@3] hid-multitouch 0003:0EEF:0005.0001: input,hidraw0: USB HID v1.10 Device [WaveShare WS170120] on usb-xhci-hcd.0.auto-1.4/input0
Compare evtest output (ABS_X, ABS_Y). It is treated by the Coreelec as an ODROID vu7 800x400 rather than a Waveshare 1024x600.
Can I do something to activate my touchscreen?
http://ix.io/2TqA (Libreelec: uname -a; lsmod; dmesg | grep WaveShare; cat /proc/bus/input/devices; lsusb -vv; cat /storage/.kodi/temp/kodi.log)
http://ix.io/2TqC (Libreelec: evtest output)
http://ix.io/2TqW (Libreelec pure: dmesg)
http://ix.io/2TqL (Coreelec: uname -a; lsmod; dmesg | grep WaveShare; cat /proc/bus/input/devices; lsusb -vv; cat /storage/.kodi/temp/kodi.log)
http://ix.io/2TqN (Coreelec: evtest output)
http://ix.io/2TqT (Coreelec pure: dmesg)