time machine broken need a fix! it shows each backup as a full backup even though it is a partial

Because the Finder only knows it's looking at hard links. And the hard links point to files that haven't been modified since the last backup and the new ones it copied for that backup. As Grant Bennet-Alder said (and I forgot to mention), for each backup, TM copies only files that have changed since the previous backup. This saves a ton of space! But the hard links for the folder for that backup point to both sets. The Finder cannot distinguish between them, and so counts them all.

To check this, you'd have to go into Terminal and run

$ cd /Volumes/LaCie/Backups.backupdb/iMac/2022-03-18-130649
$ ls ldi <some file that has not been modified since the previous backup>

$ cd /Volumes/LaCie/Backups.backupdb/iMac/2022-03-18-110742
$ ls ldi <the same file>

You may have to go a subfolder or two deeper to find such a file.

for example, substituting date/times present in your folder. You probably also have something other than iMac. Just substitute whatever you have on your system. Oh, and change "LaCie" to the name of your backup drive, too.

If you do this, and the file hasn't been modified between the times, the number in the first column will the same. That number is called the inode number and indicates a unique physical file.

>>> BE CAREFUL RUNNING COMMANDS IN THE TERMINAL. The commands cd and ls (l as in llama and s as in sierra) are safe commands to run. They will do no harm. (Actually, if you don't run sudo, you should be okay. You need sudo to do any real damage -- probably.) <<<

Time machine uses it own special "magic", working (rather like a like a database program) to fully save only the changes needed for an incremental backup, while retaining the ability to re-create the entire set of all the files present as of a given date & time.

Rather than adding another copy of files that did not change, it saves links to copies already present on the backup drive, saved on a previous date, and keeps track of it all.

To view a complete Time Machine backup, you use Time machine App (not to be confused with Time machine preferences) and it shows a display like this:

Older versions are stacked in reverse order and recede into the back of the frame.

Finder is not to be used to do any file manipulations in Time machine backups.

Finder may be telling you the size of just the saved files (incremental size) or it may be telling you the TOTAL size (if you also included all the links to older files not actually stored at that backup date)... or anything in between.

It always looks like a full backup. Time Machine works by adding a folder for each backup. In that folder are "hard links." These point to files. So when you look in a folder in the Finder, you see the files the links are pointing to. Now, some of the hard links point to files that are already on the disk that haven't changed since the last backup. So they should all look like full backups. Unless there's something else going on you haven't told us.

Starting with MacOS 11 Big Sur, the preferred format for backup drives is also APFS.

Space consumed:

I suggest you just look at space used/remaining on the drive. If overall used space on the drive is equivalent to one full backup and a bit more, your underlying issue is that it was likely showing you the composite size of each backup, INCLUDING all linked-in files.

Time consumed:

A Full backup takes all afternoon to transfer that many files. Most incremental backups are done before you notice it is running.

FWIW. Since the OP did not include the TM backup drive format type. (We only know that since they have a M1 Mac, the source drive is formatted in APFS), hard-links, may or may not, be in play here. These are only valid for backups to an HFS+ formatted drive. TM no longer uses them for backups to APFS drives.

Hard links or not, it still uses inode numbers.

Yes, there are several advanced Unix file systems in use, and I recall now that you can't list the contents of a directory anymore. So something more sophisticated is happening. NTL, the inode numbers remain.

$ ln vuc.txt ~/Documents/vuc.txt
$ ls -liog ~/vuc.txt ~/Documents/vuc.txt
2926344 -rw-r--r--  2   9904 Jan 17  2011 /Users/xxx/Documents/vuc.txt
2926344 -rw-r--r--  2   9904 Jan 17  2011 /Users/xxx/vuc.txt

Yes, this is an APFS volume, or so says Disk Utility: