iPhone 15 Pro Max to iTunes Backup over USB-C taking forever

As other apple users have noted, iPhone backups to iTunes started to take a very long time a couple of updates ago. All of the threads I could find end with some listing 5 obvious checks and closing the thread, so not really helpful at all.

I've backed up all my iPhones to iTunes since my iPhone 2 so I'm very familiar with the process. Any help is appreciated.

My set up is as follows :

• iPhone 15 Pro Max 1TB with 478GB free storage. iOS 18.6.2 (want the backup to finish before upgrading to 26)
• iMac 27" on Mojave with 72GB Ram
• 4TB Samsung Portable SSD with USB-C
• Original 60w woven 1m USB-C cable for the iPhone - iMac connection

iPhone content

• around 50 apps
• 40k photos (primary use of storage), 370Gb
• 3000 short videos
• 22Gb Music

Backing up works and has worked. But first-time seems to be running over 20 hours, which is insane given the possible transfer speeds between the different devices. iTunes also decided to do a first-time backup after I renamed my device. Sigh...

Like many other changes by Apple, this is extremely annoying. It feels like Apple is actively making this a worse experience to push people to iCloud subscriptions but I have zero intention of putting all my photos and data there.

I am at a point where I have decided to no longer update my iPhones and will likely stop buying other Apple products as well if this continues. I've gone from being a huge fan and advocate for 20 years to actively recommending friends to stay away from Apple products. Very strange place to be for a long-time fan like me.