iCloud not showing latest Whatsapp backup

I backed up my Whatsapp on my iPhone 6. I have a new ipHone 12 and have installed Whatsapp. When I try to restore from my iCloud backup, there is an old backup there but not the latest one. I've tried gong back to my iPhone 6 and backing up again, and deleting and reinstalling Whatsapp on my iPhone 12 but the same, old, backup is there.

Can anyone suggest a fix?

I'm in a similar boat, having just bought an iPhone 12 pro, and am trying to swap in a SIM from an iPhone 8.

What I've noticed is that the last backup that the iPhone 12 is recognizing was an automatic backup from last month. I think that maybe the new phones aren't recognizing manually requested backups.

I've changed my automatic backup to daily, and am going to try swapping the SIM card in again once a new auto backup has happened. Will update this post once there's a result to report on.

Someone else in a different thread recommended changing the name of your new phone to match the name of your old one, but that didn't work for me. Might be worth a try though.

Update: Switching the automatic backup to daily seems to have done the trick. I put the sim back in my old phone, changed the auto backup, and deleted Whatsapp on my new phone. After a day, I swapped the SIM back to the new phone and then reinstalled whatsapp. The Backup went as expected.

Hope this works for you!