Of course! I use handbrake with all default settings but change dimensions to 480p and then I use adapter to make it a m4v to be playable on the 3ds.
Battery usage is an absolute wreck, if it’s not plugged in you have like 15-30 minutes playtime. It definitely needs a battery bank to be truly portable but I usually use it plugged in to a wall.
Edit: it is a new 3dsxl if that changes things idk enough about the hardware.