I’m using Kubuntu 18.04 and when I use LightBurn to open a file on a USB thumbdrive I do this.
Insert the USB thumb drive and my ‘device manager’ pops open asking about accessing the partitions and I click the ‘down arrow’ icon to mount a partition. Then I start LightBurn…
Start LightBurn, go to menu File->Open
select "Computer " instead of your userID in the left pane of the file chooser dialog.
You’ll see “/” on the right pane, click that then “media” then your user ID and then the partition label.
At this point, if there is a lbrn file in the partition you should see it in the selection pane.
On Lubuntu 18.04 I noticed the USB thumb drives are automatically mounted. I will reboot into a Ubuntu 18.04 bootable ISO and see what that does and post back.
Ubuntu 18.04.3 mounts into /media/userID just like the others and I was able to install LightBurn and load a design from the USB thumb drive without problem(except missing fonts).
After plugging in the USB thumb drive, can you run this command in a terminal window and post what it shows? df -h
It’ll show you what’s mounted and will first show the device name on the left and on the far right where that partition is mounted. Pretty much everyone but Microsoft mounts disks and disk partitions into the filesystem where you specify instead of using drive letters. So if I wanted to permanently add a disk partition into my home directory I could do this:
sudo mount /dev/sdxX ~/SavedStuff
where sdx is sda or sdb or sdc as seen when you plug in the disk and look at dmesg output to show where that disk was created and named. You can use UUID names instead of you want. And the big X in the /dev/sdxX is the partition number and it too should show up in the dmesg output.