Just in case anyone else is thinking of doing this, it is possible to install a 2.5" SSD or HDD using a USB A to SATA connector with a left angled USB A extension.
Be warned it isn’t easy and there isn’t a lot of room left!
You have to heavily modify a 2.5" to 3.5" drive bay adapter and use M2 or M2.5 nuts and bolts (cut down to size) as stand offs. The drive bay is installed at an angle following the line of the laptop shell and it is wedged in using the semi transparent black cover.
This is with an RPI 3B+. I may attempt with a 4GB RPI 4B but it will be harder because the USB ports are moved around.