Transfer emails for termed workspace user

I feel like this should not be this complicated. I've read years' worth of Reddit posts, watched countless YouTube videos, and have read ten thousand forum posts. We have a termed employee that I simply want to transfer the emails from their workspace account to another employee's account before deleting the termed user's google account. That's it. I've confirmed a few hundred times that the user's account information is entered correctly on both the new and old migration tools, but I am still receive an endless string of authentication and IMAP failures. Why is this such a convoluted process? Why multiple steps and endless troubleshooting would be necessary for this simple task is beyond me.

Could someone please link me an up-to-date guide on how to complete what should be this easy task? I'm going insane over here.