Firmware 20220419 needed.
(You can check your current version in Settings - Device info - Version)
If you can't or don't want to update, there are other solutions like older Onion versions and MiniUI.
We can't take responsibility if your device is bricked in the process.
Update instructions : Here
Guest mode
Guest mode is a separate profile so you can safely lend your device to your kid or your friend.
This profile include another space where can be saved :
Saves
States
Video filter and scaling options.
Core options
Custom button remapping layouts.
RetroArch history (The Onion Launcher list will be different to reflect this.)
RetroArch playlists and favorites.
Timers for your games (Play activity app)
RGUI config (RetroArch Graphic User Interface)
Your personal files are now gathered in one place.
Your saves and most of your preferences are now in SDCARD / Saves. (Example: D:/Saves/)
This also includes your secondary profile, your config files, RetroArch lists and play activity database.
Simply copy this folder when you want to backup your data.
Miyoo audio server adoption
The audio sever lag has been removed. (Credit: Eggs)
Main UI improvments
Battery percentage is now visible on the main menu.
You can configure the battery percentage visibility and color in the theme configuration file.
It is also possible to make a theme that only shows the percentage text.
No more audio lag (Credit: Eggs)
New default theme inspired by the Lilla theme by Evolve. (Credit: DiMo)
Onionos icon by Evolve.
Textures are compression for faster results (Credit: DiMo)
Box art size fix on the included themes (Credit: DiMo)
For more information check the FAQ
Emulator changes :
New entry - DukeNukem 3D (StupidHoroscope)
New entry - Atari ST (Eggs)
New entry - Daphne (DJM)
Commodore 64 - new performant core (DJM)
Sharp X68000 - (DJM)
Jaguar - (Slow) (DJM)
Amiga is moved to console
New apps entry
MP3 player (GMU - TechDevangelist port)
Music folder : SDCARD / Media
Eggs's fake time adjuster
For RTC games.
Gamelists (Credit: Olywa123)
A gamelist file entry has been made called "miyoogamelist.xml"
If the file is present in the Rom folder, it will be effective for the following systems :
Arcade
NeoGeo
CPS1
CPS2
CPS3
Check the FAQ for more information.
Others
The default theme support asian / russian characters.
Default brightness shortcut change : Select + R2/L2 instead of Select + Start + R2/L2.
Playactivity now display asian / russian characters. (Credit : codeudan)
NES emulator : Annoying shortcut removal that changed the color palette.
The onion installer now force sort apps alphabetically.
Expert cores have been cleaned up to remove redundant/obsolete cores.
The console are renamed without the year.
Special credits on this release to Razole, DiMo and DJM, for their time and benevolent help. THANK YOU.
Also a thanks to e1000 and all the others willing to help so many people at the front with infinite patience. You are the pillars of this community. 
(V3.10.1) : Installation crash fix
(V3.10.2) : Various small fixes
Cave Story core updated to the latest
(V3.10.3) : Various small fixes
Battery percentage now allow darker fonts
(V3.10.4) : Brightness synchronization between game and main menu fix.
Credit DJM :
Updated DOSBOX Pure core
Updated FCEUMM core
Updated MAME 2003 Plus core
Updated VICE core to the last version 3.5
Updated Virtual Jaguar core
A working XRICK core (Is also included the data.zip file in the XRICK roms path)
_PUAE (Amiga), VICE (C64) and Hatari (Atari ST) now have pre-configured .opt files for the best emulation performances out of the box.
(V3.10.5) Brightness sync method universal fix.
Retroarch boot only mode audio fix.
(V3.10.6)
Onion Launcher :
1) Can now be launched from the main menu.
2) Stuck brightness value display fix.
3) Rare crash into the main menu fix.
A battery gauge is added when you turn your device off while in game.
Clock adjuster update. (Credit: Eggs, bug reported by sss888)
ScummVM update. (Credit: Stupid Horoscope) Much modern build. Bugfixes for many games.
Pokemini core update (Credit: Eggs + Shauninman) Fixes silent audio while auto loading.
Game timer fix while using the light sleep feature.
Atari 800/5200 fix. (Credit: e1000)
SG-1000 roms fix (Credit: ac3nl)
No more automatic folder creation (imgs, roms) when launching the main menu. (Credit : DJM)