I recently bought a ROG Astral 5090 BTF Edition and it doesn’t show on the devices list. When I installed Armoury Crate I was able to control its ARGB, but not the rest of my setup. I followed instructions posted on SignalRGB subreddit and updated its firmware, my Aorus Pro X870e bios, used DDU to perform a clean reinstall of the Nvidia drivers and allowed beta versions on the update section of SignalRGB, to no results. The product ID is ROG-ASTRAL-RTX5090-O32G-BTF-GAMING.
That specific GPU is a variant, but the devs can likely get it working by adding the device IDs for it to the plugin. I’d report the bug using the bug icon in the app (upper-right corner) or through this link so that the support team can follow up. 
I already reported this bug but I’m not certain that it went through because when I clicked the submit button the program closed and I got no email or any other confirmation that the report was received. I’m afraid I kind of flooded the devs with reports because I tried it a few times. Not trying to piss anyone off and already excusing myself but, if that’s the regular way the bug report system works, I would suggest to implement an automatic email for confirmation. If it’s not, maybe that’s another bug to report.
The pop-up to report the issue should close, not the whole program. That would definitely be a bug! There was also an issue impacting the ticket system from sending emails to folks indicating the ticket was received, but that got fixed overnight.
If the Report An Issue feature isn’t working, please send an email to [email protected] and include your log files found here. Sorry for the trouble!