Time Machine doing FULL backups, not incremental - how do I change that???

Mac Mini running Sonoma 14.6.1. My Time Machine drive is doing full backups of my system & external drives.

As a result, I only have 4-5 backups at any given time.

My understanding is that it should do 1 full backup, then only back up incremental changes of the orig backup, as they occur.

I can only go back 4-5 days to retrieve something , anything earlier (full backups) get erased.

I cant find any setting to alter this, what can I do?

Pretty sure its not supposed to work this way, it didn't used to...

Any help appreciated!