Don't panic, this one should be an easy fix. The red light is boot9strap trying to tell you that boot.firm is corrupted on both your SD card and internal memory. Once you took the SD out, it couldn't find an SD firm at all, so the light switched to magenta. Here's what to do:
# Back up everything on your SD card, except boot.firm and boot.3dsx
# [link|https://3ds.hacks.guide/formatting-sd-(windows)|Format the SD|new_window=true]
# [link|https://3ds.hacks.guide/h2testw-(windows)|Test the card with h2testw.|new_window=true] If it passes, continue to step 4. If not, you'll need a new SD
# (Re)Download [link|https://github.com/LumaTeam/Luma3DS/releases/latest|Luma3DS,|new_window=true] copy boot.firm and boot.3dsx to the root of your SD card, then put the card back in the ds. It should boot now
# Turn the ds off again, then see if it boots without the SD inserted. If it does, copy your files back and you're good to go. Otherwise, continue to step 6
# If the console didn't boot in step 5, find the "gm9" and "luma" folders in your backup, then copy them to the SD card.
# Hold START while booting to open GodMode9, press HOME, and select Scripts > GM9Megascript > Scripts from Plailect's Guide > Setup Luma3DS to CTRNAND
# Press A to confirm. Once the script finishes, you can turn the console off, copy your files back to the SD and your DS will be back to normal
Feel free to ask if you have any questions. Good luck!