I took some research. First of all, we must difference between arm9loaderhax and boot9strap, as they are need different files, file type and file structure. A9LH needs .bin and B9S .firm as file type. As information here the
outdated A9HL guide . And since luma build v7.1 there is no support for A9LH as entry point. So you will need for A9LH support
luma3DS version 7.05 (May 7, 2017) and also for use
godmode.bin v1.2.8 (Jul 29, 2017).
On the 2DS/3DS you need atleast access to godemode9 (thats your all in one for everything tool) at boot to get possibilitys to recover the system. So as your using A9LH verify you use the correct related file structur and files.
In worst case the screens are black and if you cant enter luma menu (hold select at boot) or godemode9 (hold start at boot) your console is bricked heavely. The last chance would be a NTR compatible Flashcard to install boot9strap,
but as you have A9LH installed iam not sure atm if this is possible without damaging the system irreparable.
No its not. The main hack is A9LH (needs .bin) or B9S (needs .firm) which will load your desired custom.firm or .bin and checks for it on specific location on your SDCard or CTRNAnd. By holding start at boot the located firm\bin in /luma/payloads/ will be loaded which is by standard godemode9. In case there are more firm\bin files located (e.g. a nativ.firm, Hourglas9.firm, Derypt9WIP.firm, Open_GBA_firm, gateway.bin) the luma chainloader menu will appear where you can choose which firm to run.
BUT you are using arm9loaderhax, in this case you need a godemode9.
bin not *.firm .
Gateway needs (very) low firmware on a 3DS and is officially only supported until 9.2. There exist a
guide for Luma+Gateway on B9S until 3DS firmware 11.2 . Latest supported version by some user modified version (Frankenstein firmware) is 11.5 or 11.7 .