Messages Are Split Between Android Phone and iPhone

I've figured it out by doing some more digging.

Hopefully, someone else finds this of use.

1. 1. From the iPhone, ensure iMessage to iCloud sync is enabled and fully synced.
   2. Perform a full backup of iPhone
   3. Factory reset the iPhone
   4. 4. On the Android download and install the Move to iOS app
   5. 5. Begin to setup the iPhone. DO NOT restore from backup. Instead set up as new while also using the migrate from Android option.
   6. Launch the move to iOS app from the Android. When at the section stage, only check the box to migrate texts. Do not migrate anything else.
   7. Once migration is done, complete the phone setup. After the setup you should only see the texts you migrated from Android.
   8. On the iPhone, navigate through the settings and re-enable iMessage to iCloud sync.
   9. iMessage will upload your Android texts to iCloud and will download your iCloud messages to the iPhone causing them to merge.
   10. Once the sync completes (could take a couple hours depending how much data you have) you can either chose to use the iPhone as is, or factory reset again but this time restore from your full backup you did in step. Since your messages are synced with iCloud, after restoring from the full backup and re-enabling iCloud message sync, all messages will be there from the merge.

Credit to lastemperor86 from Reddit here.

Note that I can confirm this method works, though my messages got duplicated unfortunately.

I found a method that works.