Preparing Transfer takes too long

I ordered and received my iPhone 12 pro max and began to transfer all of my data from my iPhone XS max via Quick Start. Given I have around 200 gigs of used up storage, I anticipated a lengthy transfer. everything is verified and I am able to use my current Apple ID but whenever it says "Preparing Transfer" on my 12 pro max, the load time is unbearable. I've only seen it make progress towards the transferring process twice; once while I let my phones do it overnight (around 6 hours) and the bar would not move. the time remaining only kept increasing, and the lowest I've seen it was at 30 minutes remaining. the other time was today at work where after 5 hours everything actually began to transfer. the lowest I've seen it was at 7 minutes and then it began to say 20 minutes. after a while, the wifi disconnected from both devices.

I have tried a hard reboot on both devices and have had trouble in the past backing my iPhone XS max to iCloud. any tips or solutions are greatly appreciated, thanks you.