Here's what I did:
-I browsed to: edge://sync-internals/
-Located "collections" at the bottom and saw my number of collections at 128.
-I clicked the three dots and created a new profile in edge browser and it generated as "profile2" (yours may different, like profile3)
-Went to C:\users\*****\AppData\Local\microsoft\edge\userdata\default\ in File Explorer
-Closed the browser
-Copied the "Collections" folder within that default folder
-Pasted the "Collections" folder into "profile2" of "userdata" (C:\users\*****\AppData\Local\microsoft\edge\userdata)
-Opened the Edge browser
-I clicked the three dots again and opened my original profile and clicked the settings wheel and selected "sign out" on the next page that came up.
-I checked "clear favorites, history, passwords..... from this device". Finished the prompt and signed out.
-This is the most important step: I went back to the home page of the browser in my newly created profile "profile2", clicked the three dots again and signed in with my original profile's credentials (email and password) while in "profile2".
-The browser did a full sync (took a minute) and kept the pasted collections from "profile2" which then all magically became my new original profile.
My collections are now synced across all of my devices, I've confirmed.
I've also saved the original "Collections" folder in safe place in case this happens ever again.
Daniel Stewart