SD-Card https://www.groovypost.com/howto/add-microsd-card-microsoft-surface-windows-rt/
This worked for me: https://openrt.gitbook.io/open-surfacert/surface-rt/linux/root-filesystem/distros/raspberry-pi-os
https://openrt.gitbook.io/open-surfacert/
https://discord.com/channels/710026735294349322/723258629033295892/864782193234018334
Hey the Surface is/was a very secure device. You need to apply different exploits in the correct order.
You can do this with the All-in-one Secureboot tool.
First you need to make sure that you don't have any KB3xxx updates installed. Easiest way to delete them is to download the official recovery image from here: https://support.microsoft.com/en-us/surface-recovery-image Format a FAT32 USB. Extract the recovery files and boot from it. Use it to reset your device.
Now you can apply the goldenkey GK exploit. Based on GK you can apply the yahallo secureboot exploit. Now you can/should remove GK since it made some trouble with win10 on some devices.(sRT2 iirc)
Now you can boot any ARM32 efi app like grub, Linux UEFI Stub kernel, ... You can place the rootFS either on USB or SD card. If you use windows you don't have native ext4 support which makes it hard to work with the rootFS. One way to get the job easily done is to use the Raspberry pi Image writer and an official raspberry pi Image. This will write a FAT32 and EXT4 partition to your USB. You don't need to care about the EXT4 part at this point. You only need to replace the contents of FAT32 partition which can be done by Windows.
You can find the new content for your FAT32 partition here: https://openrt.gitbook.io/open-surfacert/surface-rt/linux/efi/prebuilt-binaries (UEFI shell + startup script for linux boot)
Once your USB drive is prepared you turn off you Surface plug the USB driver in your Surface. Press and hold VOL-Down. Tap Power. And release Vol-Down ~5-10s after the Surface logo showed up. Now you need to wait around 30-60s since raspi Os on USB isn't the fastest and we don't have early display access right now. Now you should see the RaspiDesktop.
Now you need to expand your RootFS: https://openrt.gitbook.io/open-surfacert/surface-rt/linux/root-filesystem/distros/raspberry-pi-os#todo-after-boot