Use boot-repair. I had the same issue just the other day. I've been running a stable Ubuntu system for several weeks. I shut it down and everything seemed normal. Next day I attempted to boot and got the same message you did, "No boot device found. Press any key to reboot." I figured my hard drive died. Actually it was just a boot issue that was fixed using boot-repair. I booted to my live Ubuntu on USB stick. I opened a terminal and entered the following commands:
sudo add-apt-repository ppa:yannubuntu/boot-repair
sudo apt-get update
sudo apt-get install boot-repair
boot-repair
After running boot-repair everything was back to normal. I still have no idea what happened to cause the problem, but since it was relatively easy to fix I'm not seriously concerned.
Note: Boot-repair appeared to freeze during the actual process of resetting GRUB and several error messages appeared in my terminal window regarding boot-repair. Eventually boot-repair completed it's work and gave a report that included errors. And then I rebooted my system and it worked like a charm.
boot-repair
? – totalynotanoob Oct 26 '20 at 07:49