I've found the solutions on my Garuda and Resolve Studio with an AMD GPU.
First issue:
Not starting et all, black windows instead of footage if started.
Solution:
Install the AMDPro drivers and start with this command prefix "progl":
progl /opt/resolve/bin/resolve %u
How to install AMDgpu Pro drivers (even if you don't have an AMDPro GPU) pls check the ArchLinux Wiki.
Second Issue:
Missing Top Menu (conflict with Latte)
Solution:
For the missing top menu of DaVinci Resolve (or any program which is in a familiar conflict with latte) there is this solution (combined with the AMDPro drivers) use this command:
killall latte-dock && progl /opt/resolve/bin/resolve %u & sleep 30 && latte-dock --replace &
Since Resolve has some issues with the Latte-dock implementation. You can change the sleep as you see fit. Since it actually seems to count for the Project Manager window in the first place. I felt like 30 seconds are enough for me to decide which project I want to load 
If you are within Resolve your Latte dock will restart, as the commands tells it to and you can see your TOP menu in Resolve like in the Windows version.
The idea of this solution is to kill latte until Resolve has started which avoids the initial conflict with the top menu. Bear in mind the project manager window is part of the starting process of DaVinci Resolve.
I hope that helps everybody who is considering using Resolve (or any other tool which might have issues with latte). I've seen the issue often and a pretty old reddit post gave me the solution and I modified it ofc
Regards,
Bruce
P.S.: I hope I don't get smacked for reviving but it seems to be a pretty important issue. I found a ton of requests of them across the net for all distributions. (which mostly use Latte or got issues with missing AMD GPU pro drivers). Since Latte is part of (at least) the Dr460nized version of Garuda I think this solution should be here to be found.
EDIT: Minor corrections, added ArchWiki-HLink