Is there a generic way to boot the installed OS using a usb device?

I have tried to install Lubuntu 18.04 on an Acer Switch 3 (which allows only EFI boot, has no legacy mode). For more than a week I have not managed to make the system start.

Today I have restarted the tablet after a long time, and very suprisingly, Lubuntu has booted immediately. Then, after a lengthy update, I was asked to restart, and now it does not start anymore. Instead I get the message

Default Boot Device Missing or Boot Failed. Insert Revocery Media and Hit any key Then select ‘Boot Manager’ to choose a new Boot Device or to Boot Recovery Media

Since the system is there, I would like to boot it nevertheless. Unluckily, I forgot to create a boot media.

So this is my question: Is there any “generic” way to boot the installed system using a usb device? A tool or something that can analyze the disk and reckognize a bootable OS?

Thanks in advance!