If you go to Settings > Advanced – what is the “AnkiDroid directory” set to in your main version? Is it /storage/emulated/0/AnkiDroid?
Change that to /storage/emulated/0/Android/data/com.ichi2.anki/files/AnkiDroid. It should have changed over automatically, but storage migration has been skipped for some users [Storage Migration FAQ · ankidroid/Anki-Android Wiki · GitHub].
The point is that both the alternate Anki and the main Anki are going to sync to the same AnkiWeb account. You used alternate Anki to get the data there, and you’re using main Anki to get the data back. Then you won’t need alternate Anki anymore.
So for now, as long as you sync when you open and when you close the app, your collection will always be in sync.
Will you do me a favor when you get all of this settled? Go to Settings > About > Copy debut info – and paste that here. It’s still a puzzle why Storage Migration is getting skipped for some users, so that might be helpful.