Under settings, there's an option for "Naming Management" where you can set the Folder Name and File Name. Originally, Action 3 stores files in the folder "DJI_001". You don't have to change anything and you can just store files in this default folder until the end of times. So far so good.

If you go to Naming Management and create a folder with the extension, say "A01", then the next file will be stored in the folder "DJI_002_A01". Notice that instead of "DJI_001_A01" the number (after DJI_) got also incremented to "DJI_002..." So every time you create a new folder extension (eg, _BB1, _CC2, etc) the number in "DJI_XXX" will also be incremented by one.

So try this...

1. Create a custom folder name "A00" and take a photo. This photo will reside in the folder "DJI_002_A00".
2. Create a custom folder name "A01" and take a photo. This photo will reside in the folder "DJI_003_A01".
3. Create a custom folder name "A02" and take a photo. This photo will reside in the folder "DJI_004_A02".

Thereby creating folders where only the custom extension changes but the DJI_001 number part stays the same is not possible, eg:
DJI_001_A00
DJI_001_A01
DJI_001_A02
DJI_001_A03
etc

Maybe I'm not seeing something right but I don't understand why change/increase both the "DJI_XXX" number part AND the folder extension, too, at the same time?

Also, when you want to create a new custom folder extension and you tap on the green checkmark, you will get a confirmation message that the new files will be stored in "DJ_XXX_YYY" folder. However, there's no option to cancel this. The only thing you can do is confirm it. And once you did, there's no way to go back. Your new files will be stored in the new folder whether you want it or not, even if you click the Trash icon next to the folder name management.

I got no use  for Folder naming I got use for File naming.   but thanks for trying to explain that. DJI had the good name of DJI_001 on the action one, now we got too much info on the file today if asked  IMHO

OA3 starting to feel like Gopro, terrible file naming + touch screen is too sensitive for me

About filesnames, DJI_001 is good but could also be OA3_001 to make it more logical for all parts

Agree I rather get a gopro  then  have DJI try to be a  gopro

The long file name is date and time related and I seem to be able to sort by when they were taken - which is something I never managed with gopro in the past.
It could be better and if you have e.g. a mini3 or pocket 2 also starting with DJI they get muddled together more than you would like.