https://ubuntuforums.org/showthread.php?t=2358003
Here's the gist:
This probably also applies to other Acer models using InsydeH2O BIOS. After much messing around, this is how I got dual boot working on my Acer Aspire R14-471T:
1) Update to the latest BIOS (I know, it's UEFI, but I'm going to call it a BIOS). My new laptop shipped with 1.07, 1.10 is the latest as of this posting.
2) Shut down, then while starting back up hit the F2 button many times until the BIOS Setup Utility loads.
3) In the "Main" menu, set the "F12 Boot Menu" option to "Enabled". Press F10 to Save and Exit, then once Windows loads shut down again.
4) Insert your USB flash drive with your 64-bit Ubuntu installer on it.
5) Power on and keep pressing F12 until the boot menu pops up. Select the flash drive, boot, and install Ubuntu.
This is where things get tricky:
6) After ubuntu reboots, it will boot back into Windows. Shut down again. Reboot and hit F2 to enter the BIOS again.
7) Under "Security", choose "Set Supervisor Password", and set one. You will need this password any time you go back into the BIOS. A bunch of options on the page should change from grey to blue.
The "Select an UEFI file as trusted for executing" should now be available. If it's not available, check that Secure Boot is still Enabled, if not, Enable it. Select it, and navigate to HDD0->EFI->ubuntu->grubx64.efi. The BIOS will ask you for a name for it, I called it Grub.9) Hit F10 to save and exit, then immediately hit F2 again to re-enter the BIOS.
10) Now go to "Boot", set "Secure Boot" to "Disabled", and arrow down to the bottom of the list to your new "Grub" entry. Hit F6 until it's the top of the list.
11) Hit F10 one last time. Your system should now reboot to the Grub boot loader!
Note that the instructions on setting a trusted UEFI file are also necessary in non-dual boot situations.