2) Setting a Quick Menu button combination:
2.1) Settings > Input > Hotkeys > Menu Toggle Controller Combo > Set whatever you want
2.1.2) Main Menu > Configuration File > Save Current Config
3) The guide will now be divided based on whether you want your ROMS internally (16GB limit on Xbox One, 30GB limit on Series S/X)
Note: For both internal and USB it's recommended to have a folder structure as follows:
Internal
==========
3.1) Go to Import Content and select Scan Directory for ROMs without extensions like .iso, .bin, .chd, etc. (We'll get to them later.)
3.1.1) Press A on the very bottom option (Q:\Users\UserMgr0.....
3.1.2) Select your ROMs folder here and press Scan This Directory.
USB
==========
3.2) Go to Import Content and select Scan Directory for ROMs without extensions like .iso, .bin, .chd, etc. (We'll get to them later.)
3.2.1) Press A on the D:\ drive and select your ROMs folder (or Scan This Directory if they're on the root of the drive).
4) Scanning ISO, BIN, CHD, etc:)
These will commonly NOT scan with Scan Directory / Scan File, these are common files shared across many cores, so we need to specify what core to use with them.
4.1) Go to Import Content and Manual Scan
4.1.1) Use the above 3.1.1 & 3.1.2 or 3.2 & 3.2.1 steps to navigate to your ROMs folder
4.1.2) This is where the folder structure is necessary, go inside the folder with your ISOs / CHDs, or whatever for one console, I'll use PS1 as an example here.
4.1.3) Press Scan This Directory
4.1.4) Select the System Name or create a custom one if you want.
4.1.5) Set the default core you want to use for these ROMs
4.1.6) Go into File Extensions and type the extensions of your ROMs in the folder (iso, chd, etc)
4.1.7) Press Start Scan
4.1.8) Repeat for all other folders with commonly shared file types.
5) Saving your core config for a core that crashes when you press Close Content:
Settings > User Interface > Show Advanced Settings ON
Menu Item Visibility > Quick Menu > Show 'Flush Options to Disk' ON
Now when you launch a core, go to the Quick Menu > Options > Manage Core Options > Whichever option suits you.
6) Customising RetroArch:
6.1) Changing the Menu Driver (overall look):
Settings > Drivers > Menu > Choose your desired menu driver
Then go to Main Menu > Configuration File > Save Current Config and restart RetroArch.
6.2) Changing the appearance of the selected menu driver:
Settings > User Interface > Appearance > Menu Color Theme
There are also other settings you can play around with here.
Once again, make sure to save your Configuration File, as shown above.
Warning:
Make backups of your saves often!
Console updates, as well as app updates, can remove RetroArch from your Xbox.