Copying Time machine Files from old HDD to new HDD

Hi all, I am really struggling with moving time machine backups from an old hdd to a new one. My old HDD is nearing 15 years and so I want to preserve the files on it, so I've been trying to move the files to a new HDD. I understand that it is difficult, if not impossible to actually use the same time machine files as a backup in the future, but I simply want to preserve the files on it so I can access them if need be. I thought it would be a simple drag and drop but I keep getting the error that 'this backup format is not supported.' I assume it's because the old backups were made using Mac OS Extended instead of the new AFPS. I got around this by going into the backup folder and just drag and dropping the 'Macintosh HD' file, which provided no issues. But now my latest issue is that i have about 9 backups on the 1tb HDD, but each and every backup is almost 500gb in size which doesn't make sense. I assume obviously it's to do with time machine settings, but i want to port everything over to the new HDD, but how can i get only the initial backup and the changes between the following 8 backups? Chatgpt is telling me to use a resynch function but wanted to get opinions first. Many thanks