Welcome @User1 to OpenMandriva Forum and community.
For support try posting ALL OF the exact error you are seeing.
[Forum] How to post code as code
The amdgpu driver is a kernel module, to my knowledge, there should be nothing to install or enable. If you get a graphical desktop using startx then it sure would seem that graphics is working meaning amdgpu driver is working.
The repos are name main, extra, non-free, and restricted. I do not know what AMDGPU Repo even is. And I do have AMD graphics. My graphic hardware:
$ inxi -G
Graphics:
Device-1: Advanced Micro Devices [AMD/ATI] Barcelo driver: amdgpu v: kernel
Device-2: IMC Networks USB2.0 HD UVC WebCam driver: uvcvideo type: USB
Display: x11 server: X.org with: Xwayland v: 24.1.9 driver: X:
loaded: modesetting dri: radeonsi gpu: amdgpu resolution: 1920x1200~60Hz
API: EGL v: 1.5 drivers: kms_swrast,radeonsi,swrast
platforms: gbm,x11,surfaceless,device
API: OpenGL v: 4.6 compat-v: 4.5 vendor: amd mesa v: 25.3.4 renderer: AMD
Radeon Graphics (radeonsi renoir ACO DRM 3.64 6.18.7-desktop-2omv2590)
API: Vulkan v: 1.4.341 drivers: radv,llvmpipe surfaces: N/A
Info: Tools: api: clinfo, eglinfo, glxinfo, vulkaninfo de: kscreen-console
wl: wayland-info x11: xdpyinfo, xprop, xrandr
Edit: I may not fully understand the problem but it sounds more like something wrong with sddm or something with authentication. The output of dmesg orjournalctl is likely to tell us what the problem is. To start with lets get the output of dmesg like this:
dmesg > dmesg.txt
That creates the file dmesg.txt which you can post here. You want to do this after a boot that did not automatically boot to graphical desktop. Let’s see what that tells us.