Welcome to the clan of gamers who believed that they had bought a smartphone of gamers, at the time I based myself on the software and hardware ecosystem of the Rog series, I could still buy the Rog 3 new and these accessories, I still bites the .......... for not having done it.
For the 5 series, there is only the Kunai, which among other things brings nothing compared to the compatible ones and which is excessively expensive.
There is also AeroCooler which is only usable for triggers with light games.
The two best Rog 3 accessories do not exist, one is not compatible, the other is not found, see it was never made
Worse, the software functions, the live stream has been removed (fortunately, third-party solutions work very well), as for the key mappings, also removed, there is no alternative solution to be able to use a third-party dock and map the keys .
For the hardware here is a post, there is also some with a moderator's answer for the key mapping, I haven't found it but it's absolutely certain.
https://zentalk.asus.com/en/discussion/comment/182332#Comment_182332