Reset to Single Partition after DiskUtility BOOTCAMP partition removal

Hello all. I would appreciate any help in fixing up my P.E.B.C.A.K. error that you can suggest. I've exhausted the support I can find on the apple support articles, and my google-fu skills, but maybe I'm not searching the right thing. I would be grateful if someone can point me in the correct direction. to restore my

Preface: I have a Time Machine Backup from minutes before I started to mess around with doing anything with Boot Camp.

(1) My Mac

iMac (Retina 5K, 27-inch, Late 2015)

macOS High Sierra version 10.13.6 (15G66)

NOTE: I do not want to upgrade the OS due to legacy applications that I use daily not working in newer mac OS versions (as tested by the application community)

(2) What I did to mess things up:

- Attempted to install windows via boot camp assistant and ran into the problem where the new windows 10 ISOs have files too large for the default FAT32 boot camp assistant partition formatting

- Followed this guide to split the ISO. https://twocanoes.com/using-larger-windows-10-isos-with-boot-camp-assistant/

- Successfully used Boot Camp Assistant to make a 100GB windows partition using the split ISO

- Decided that I didn't want like the rebooting and rebooting and rebooting of switching between the windows and mac OS.

- DID NOT READ THE WARNINGS

- From macOS, using Disk Utility, I erased the BOOTCAMP partition. I was expecting this to be like normal partition removals and that my Macintosh HD would be re-sized to the full 1TB internal HD size.

- This did not happen.

(3) My recovery attempts:

- Ran Disk Utility First Aid. No issues found.

- Attempted to see if Boot Camp Assistant (after some googling and "oh-no's") would let me undo the partition. It would only let me make a new partition.

- Booted into recovery mode and performed:

- Disk Utility first aid (no issues found).

- Macintosh HD erase and restore. Use Disk Utility to erase an Intel-based Mac - Apple Support

- Rebooted my computer and got the white "do not enter" circle with a line thru it symbol.

- Mac OS re-install per How to reinstall macOS - Apple Support which did not work. Right when it completed the install it threw an error and kicked me back to the equivalent step 1 screen from this article (due to the age of my OS and computer)

- Attempted the Mac OS re-install again with the same results.

- Without rebooting, I then gave up and hoped that I could get my computer somewhat functional again and performed the Time Machine Backup Restore which was successful.

(4) Current state of affairs.

- When I look at Disk Utility Partitions, I see Macintosh HD is 920GB and that while visually there isn't the normal partition view in the pie chart, there does appear to be a differently shaded slice that was about the 100GB size of my deleted BOOTCAMP partition.

- When I use terminal to look at things I don't see anything that looks like BOOTCAMP or my missing 100GB floating around somewhere under a different name. Note: the external 4TB drive is my Time Machine drive.

diskutil list
/dev/disk0 (internal):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                         24.0 GB    disk0
   1:                        EFI EFI                     314.6 MB   disk0s1
   2:          Apple_CoreStorage Macintosh HD            23.6 GB    disk0s2
   3:                 Apple_Boot Boot OS X               134.2 MB   disk0s3

/dev/disk1 (internal, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *1.0 TB     disk1
   1:                        EFI EFI                     209.7 MB   disk1s1
   2:          Apple_CoreStorage Macintosh HD            897.4 GB   disk1s2
   3:                 Apple_Boot Recovery HD             650.0 MB   disk1s3

/dev/disk2 (internal, virtual):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:                  Apple_HFS Macintosh HD           +920.0 GB   disk2
                                 Logical Volume on disk0s2, disk1s2
                                 6E79FC79-54C9-4799-9D3A-AD112E3CC45F
                                 Unencrypted Fusion Drive

/dev/disk3 (external, physical):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                        *4.0 TB     disk3
   1:                        EFI EFI                     209.7 MB   disk3s1
   2:                  Apple_HFS Untitled                4.0 TB     disk3s2

I would appreciate any wisdom and recovery steps that you can think of.