Clean Install; No apps added as yet. Live Boot and 1st install has display on both monitors. I only have to swop their positions to match the physical layout.
When I allow the "discover" package manager to update my system it downloads about 100mb, reboots.
When I log back in my left monitor now has a black desktop background, the right is normal, I am able to mouse to the left monitor and drag apps there without issue, only the background has disappeared. Switching between themes or different backgrounds applies the theme to the right monitor only.
Operating System: KDE neon 5.23
KDE Plasma Version: 5.23.4
KDE Frameworks Version: 5.88.0
Qt Version: 5.15.3
Kernel Version: 5.11.0-41-generic (64-bit)
Graphics Platform: X11
Processors: 8 × AMD Ryzen 3 3100 4-Core Processor
Memory: 15.6 GiB of RAM
Graphics Processor: AMD Radeon Pro W5700