@quanghieuci Hi 🙂

Since recalbox 4.0.0 the system is read only:
https://github.com/recalbox/recalbox-os/wiki/Make-a-partition-writable-(EN)

Here you will find some more information about getting root access:
https://github.com/recalbox/recalbox-os/wiki/Root-access-on-terminal-(EN)

You can try to get the preferred mode of your TV with the command: tvservice -m CEA
https://github.com/recalbox/recalbox-os/wiki/Video-configuration-detailled-(EN)

If something does not work, then just ask again 🙂

Regarding your second question: Afaik there is no 3DS available at the moment.

recalbox não emula nintendo ds, nem tão pouco 3ds.