I suggest that we add a menuentry for persistence into the default configuration files for grub and syslinux in the Lubuntu iso files. This would make it straightforward to get a persistent live Lubuntu system directly by cloning the iso file.
You have probably already noticed that when you boot a USB drive cloned from an iso file of 20.04 LTS, a partition with the label
writable will be created. In the default ‘live’ case it is used to store logs (and maybe dump files) in order to help debug problems during booting and installing.
And if you add the boot option
persistent the system will become a persistent live system, where you can install programs and save files in your standard directores (Documents, Downloads, Music, Pictures …) and they will survive shutdown and reboot.
So with an extra boot option in the grub.cfg and txt.cfg files, the user will get the option to run the default cloned drive not only live-only but also persistent live. This can be achieved with mkusb now, but most end users will never install it, they will probably not even know about it. But the standard Ubuntu Startup Disk Creator is there for cloning.
The boot menu can look like this:
syslinux menu in BIOS mode:
grub menu in UEFI mode:
Find more screenshots in post #8.