Common In Some Acer Computers, if after installation you see No bootable device this means your newly installed operating system (OS) isn't being recognized. to fix this, repeatedly press F12 and boot menu Will show up, Probably Security Tab Is where "Select an UEFI File as Trusted For Executing" appears, to get to security tab first move with arrow keys move with right arrow to get to security tab then click down arrow to move to "Select an UEFi File as Trusted For executing" click enter after you move to it, and then you'll see your storage like emmc for EMMC ssd for idk ssd or sata click on it and then move with down arrow keys to move to ubuntu then enter, and you'll see many options move with down arrow again and select the "shimx64.efi" and name whatever you want for the thing example: LinuxMint, click enter again enter and now move to boot and then you'll see your named uefi file now go with arrow keys to select your own named uefi file, now click f6 and click until it is in the top. now its done! click ESC and then Ok or save it using arrow keys to navigate to "Exit" then save.