Update:

I discovered that the board I have has different IDs. I've updated the rules to reflect that, but still no joy.

Added rules:

# Added 20230604 to match MH-ET Live ATTiny88
# Vendor  ID: 1A86
# Product ID: 7523
SUBSYSTEMS=="usb", ATTRS{idVendor}=="1a86", ATTRS{idProduct}=="7523", MODE:="0666"
KERNEL=="ttyACM*", ATTRS{idVendor}=="1a86", ATTRS{idProduct}=="7523", MODE:="0666", ENV{ID_MM_DEVICE_IGNO
RE}="1"

@Pavel

I have tried adding the udev rules, but even after restart, the board is not recognised. The output from dmesg is below.

Any suggestions?
TIA

[ 1669.101501] usb 1-6: new low-speed USB device number 33 using xhci_hcd
[ 1669.257640] usb 1-6: device descriptor read/64, error -71
[ 1669.497114] usb 1-6: device descriptor read/64, error -71
[ 1669.733502] usb 1-6: new low-speed USB device number 34 using xhci_hcd
[ 1669.889674] usb 1-6: device descriptor read/64, error -71
[ 1670.133624] usb 1-6: device descriptor read/64, error -71
[ 1670.244484] usb usb1-port6: attempt power cycle
[ 1670.893581] usb 1-6: new low-speed USB device number 35 using xhci_hcd
[ 1670.921586] usb 1-6: Device not responding to setup address.
[ 1671.156627] usb 1-6: Device not responding to setup address.
[ 1671.365514] usb 1-6: device not accepting address 35, error -71
[ 1671.493172] usb 1-6: new low-speed USB device number 36 using xhci_hcd
[ 1671.521115] usb 1-6: Device not responding to setup address.
[ 1671.757522] usb 1-6: Device not responding to setup address.
[ 1671.965525] usb 1-6: device not accepting address 36, error -71
[ 1671.968370] usb usb1-port6: unable to enumerate USB device