Solved:

In the BIOS settings, there was an option to "enable EFI file as safe" or something. It was greyed out so I set a BIOS admin password to unlock it. I then clicked it, selected HD0 -> grubx.efi. After confirming it brings you back to the option screen. I then disabled secure boot (I swear I disabled this before...), moved the new grub EFI option to the top of the boot order and voila!

How I should have installed Windows for dual boot

this answer (personally haven't tried it) or if you want to partition your drives using ubuntu for some reason like I did...

1. (Assuming you are starting on Linux) get two flash drives. Put your windows image on one [windows tutorial] and ubuntu on the other [ubuntu tutorial]
2. Restart and launch into your Live USB Linux
3. Partition drive using gparted into your desired size. Change master boot record [MBR] to GUID Partition Table [GPT] using gdisk if your drive is not GPT already
4. Restart and launch windows installer. Complete the install
5. Restart. If your computer just launches into windows, you will need to use boot-repair to fix grub

My boot-repair pastebin link

Tried:

1) Everything here:

• Repair from Windows – Command Prompt bcdedit /set {bootmgr} path \EFI\ubuntu\shimx64.efi
• Disable Fast Boot
• Use Boot Repair tool
• Windows 10 and Ubuntu are installed in different mode Partition/boot/efi box checked

2) Disabled secure boot

Installing procedure:

1. Start with Ubuntu 19.10 on 1TB SSD and an empty 4GB USB drive
2. Downloaded an Ubuntu 19.10 image and put on USB drive using startup disk creator
   • Also downloaded a Windows 10 image. Would later put on USB drive using woeusb
3. Restart and launch into Live USB Linux
4. Partition using gparted. sda1 linux, sda2 NTFS and empty. Use gdisk to convert drive from MBR -> GPT
5. Restart into Ubuntu. Swap linux image for windows on USB
6. Restart and launch into windows installer. Complete install

--- Now I cannot access Ubuntu. If I boot with UEFI I get windows, if Legacy I get a black screen ---

7. Re-download linux image. Swap windows image for linux on USB using rufus
8. Restart into Live USB Linux. Run boot-repair according to 1) above

Notes:

• I used Legacy instead of UEFI to boot into Ubuntu before all this. UEFI would not boot
• Password managers are a life saver. One user/password to access any account when working on fresh installs so much
• Acer aspire R7-371T

Here is a snapshot of my current drive partitions

To try:

• Found this seemingly complete solution while writing this
• This requires a full re-install of my ubuntu partition but I will install ubuntu in uefi mode

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