iPhone 16 pro max syncing issues…..

Get with Apple support and don’t give up and DO NOT wipe your old phone or do anything to it until you can get iCloud straight.
Sounds like database got corrupted. I went through this with archiving and they lost all my text attachments. I absolutely hate iCloud forever for it but lesson learned. I’m just missing hundreds of contacts and hundreds of old sexy pics from crazy exes back in the day. Also don’t keep important things in your text DB.

Neither. It just started archiving old text attachments. I don’t know how fast I caught it because when I noticed, I still had 4 months or so worth of attachments and everything before that wouldn’t download. Always had iCloud set to save everything and paid for extra cloud storage. I was receiving hundreds of hi res images via sms and iMessage around that time due to a big project where we were documenting otherwise undocumented parts deep inside hydraulic systems due to a possible qualification flaw. Danced with Apple support for months but always got the run around and pushed into endless circles. Same on multiple devices. Attachments show as available but won’t download and just error out.
Having a Mac may have allowed for trying to repair the db file. I gave up.
Oops wrong reply but that’s what happened to me.