No option to load Windows after dual boot

Hello. I am brand new to Ubuntu, and I am trying to install Ubuntu 18.04LTS alongside my Windows 10. I installed Ubuntu successfully, but I can't find an option to choose to boot Windows or Ubuntu on startup; It just goes straight to Ubuntu. Allow me to share with you my journey, and please help me fix my problem.

I fist installed Ubuntu by following the instructions here: https://www.youtube.com/watch?v=qNeJvujdB-0
The "Install Ubuntu alongside Windows 10" option did not show up, so I followed the instructions to partition files for "Something Else". My initial free space partition was 80GB, I created a 16GB swap space partition, then left the remainder for \ directory (like is shown int he video).

After trying to install, it created a "grub-efi-amd64-signed" package failed to install error. I started the install process again, followed the instructions here (https://askubuntu.com/questions/1028703/the-grub-efi-amd64-signed-package-failed-to-install-target) (second answer down), telling me to create a 1GB EFI System partition as well, and the error did not occur again.

I was now able to boot Ubuntu, but unlike in the original video, where starting the computer brings you to a menu which lets you choose Windows or Ubuntu, I was just loaded straight into Ubuntu and was unable to find an option to boot Windows instead.

First, I tried following the instructions here: https://www.youtube.com/watch?v=sueumjgGFkA
My output for "sudo fdisk -l" looks like this:
---------------------------------------------------------------------------------
Disk /dev/loop0: 3.7 MiB, 3887104 bytes, 7592 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop1: 2.3 MiB, 2433024 bytes, 4752 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop2: 86.9 MiB, 91099136 bytes, 177928 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop3: 14.5 MiB, 15196160 bytes, 29680 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop4: 140.9 MiB, 147722240 bytes, 288520 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop5: 34.7 MiB, 36323328 bytes, 70944 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop6: 478.2 MiB, 501374976 bytes, 979248 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/loop7: 13 MiB, 13619200 bytes, 26600 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes

Disk /dev/sda: 465.8 GiB, 500107862016 bytes, 976773168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x46edf808

Device Boot Start End Sectors Size Id Type
/dev/sda1 2048 807214211 807212164 384.9G 7 HPFS/NTFS/exFAT
/dev/sda2 974987264 976766975 1779712 869M 27 Hidden NTFS WinRE
/dev/sda3 807215102 974987263 167772162 80G 5 Extended
/dev/sda5 * 807215104 809213951 1998848 976M ef EFI (FAT-12/16/32)
/dev/sda6 809216000 841213951 31997952 15.3G 82 Linux swap / Solaris
/dev/sda7 841216000 974987263 133771264 63.8G 83 Linux

Partition table entries are not in disk order.

Disk /dev/sdb: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 4096 bytes
Disklabel type: dos
Disk identifier: 0x493d9c20

Device Boot Start End Sectors Size Id Type
/dev/sdb1 * 2048 1953521663 1953519616 931.5G 7 HPFS/NTFS/exFAT

Disk /dev/sdc: 931.5 GiB, 1000204886016 bytes, 1953525168 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: gpt
Disk identifier: 5A236829-9B5D-474A-847B-D0AD7031BAED

Device Start End Sectors Size Type
/dev/sdc1 34 262177 262144 128M Microsoft reserved
/dev/sdc2 264192 1953523711 1953259520 931.4G Microsoft basic data

The backup GPT table is corrupt, but the primary appears OK, so that will be used.
Disk /dev/sdd: 3.7 TiB, 4000787029504 bytes, 7814037167 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 4096 bytes
I/O size (minimum/optimal): 4096 bytes / 33553920 bytes
Disklabel type: gpt
Disk identifier: B507B947-051E-4B38-A706-3C8486DFD234

Device Start End Sectors Size Type
/dev/sdd1 34 262177 262144 128M Microsoft reserved
/dev/sdd2 264192 7814035455 7813771264 3.7T Microsoft basic data

Partition 1 does not start on physical sector boundary.

Disk /dev/sde: 7.2 GiB, 7746879488 bytes, 15130624 sectors
Units: sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disklabel type: dos
Disk identifier: 0x051a159a

Device Boot Start End Sectors Size Id Type
/dev/sde1 * 2048 15130623 15128576 7.2G c W95 FAT32 (LBA)
-----------------------------------------------------------------

then my output for "sudo update-grub" is this:
----------------------------------------------------------------------
Generating grub configuration file ...
Found linux image: /boot/vmlinuz-4.15.0-36-generic
Found initrd image: /boot/initrd.img-4.15.0-36-generic
Found linux image: /boot/vmlinuz-4.15.0-29-generic
Found initrd image: /boot/initrd.img-4.15.0-29-generic
Adding boot menu entry for EFI firmware configuration
done
---------------------------------------------------------

As you can see, it doesn't see where my windows partition is, and there is no change in how the computer boots.

The next thing I tried are the instructions here: https://help.ubuntu.com/community/Boot-Repair
Specifically, the "Recommended repair" option; I don't know what to do in the Advance options
I tried this a few times, and there is the most recent pastebin output: http://paste.ubuntu.com/p/SBt7mt4t62/
Again, no changes. However, the final window did say something regarding the boot files being far from the front of the drive.

Another thing I have tried is shuffling the boot order of my drives (which includes "ubuntu", the flash drive I used to install it, and the hard drive with my Windows on it), but it has had no effect. Furthermore, when I go back to the BIOS, it always reverts back to having "ubuntu" at the top of the boot order.

I'm not sure what to do next, so I've decided to reach out for help to be able to choose which OS to use.
If all else fails, I would at least like to use Windows again.