@chaperone5986 These cards were never supported officially.
I own P360 Tiny. There is definitely some integration code in BIOS that works with officially supported NVIDIA cards. At least BIOS is smart enough to control system (CPU) fan when NVIDIA GPU overheats (one of officially supported cards comes with just heatpipe and small heatsink that is cooled down by CPU fan). See this post for details:
https://forums.servethehome.com/ind...o-reference-thread.34925/page-114#post-456292
Also even with officially supported NVIDIA card if you choose primary GPU as 'IGD' (Integrated) for some absurd reason NVIDIA card disappears from system. And yes, it'll still consume power and turn on fan. I've created topic about this here:
English Community-Lenovo Community
I'm sure that it's just buggy BIOS implementation. And since Lenovo don't want to fix it for officially supported GPU, I'm sure they will just ignore you with RX6400.. Sorry..
I can suggest you to try changing this 'Primary GPU' BIOS setting. But it could happens that this system is so stupid that there will be no way to revert this setting at all (unless you have supported NVIDIA card laying somewhere to plug it temporary).
Another thing to try is to use 4x riser. I know it sucks and much worse than 8x, but it could happens that this will 'workaround' this logic in BIOS that disables GPU based on BIOS settings.. But keep in mind that this is gray and untested area...
I think that I'm extremely lucky that I decided to not try AMD graphics with this machine. 90% of times I need external GPU only to pass it to Windows VM. So my first idea was to purchase that RX6400 card just becuse AMD works much better under Linux.. But I decided to stay with NVIDIA because of potential "error 43" error with AMD Windows guest drivers.. Now I see that it's not that easy at all..
I know for sure that P350 Tiny has no such issues... At least with official GPU. So if it's critical you man want to just downgrade..
In any case please let me know how it goes.. If you'll be able to solve it somehow I'll try to repeat this..