Update - I have an old DSi that I can use to test this out. This is a result I saw -
The new R4i Upgrade tries to auto-boot on the DSi but gets a firmware error. At least its showing up unlike on my 3DS where it is neither visible on the home menu or in TWLauncher.
The R4 card that I personally own works on the 3DS but does not show up on my old DSi
EDIT: I was able to get the latest firmware on the R4i card, and it boots up properly on the DSi. But it still doesn't show up on the Luma N3DS. But the older R4 does? I wonder why.
Forgive my ignorance. 3DS/DS cfw and hacking is something I step away from for months so I forget how I achieved certain feats in the first place