SUMMARY
After updating to KDE 6.4.5 on CachyOS (Wayland, NVIDIA driver 580.82.09 open‑source), all games launch only in borderless mode. Fullscreen mode does not work, and the refresh rate option (e.g., 240 Hz) is locked. Issue was not present in KDE 6.4.4.

STEPS TO REPRODUCE
Install CachyOS with KDE Plasma 6.4.5.

Use Wayland session with NVIDIA open‑source driver 580.82.09.

Launch any game and attempt to switch to fullscreen mode and change refresh rate.

OBSERVED RESULT
Games launch in borderless mode only.

Fullscreen mode cannot be enabled.

Refresh rate setting is locked and cannot be changed to 240 Hz.

EXPECTED RESULT
Games should be able to run in fullscreen mode.

Refresh rate should be adjustable (e.g., to 240 Hz).

SYSTEM INFORMATION
Linux Distro: CachyOS (fully updated)

KDE Plasma Version: 6.4.5

KDE Frameworks Version: 6.18.0

Qt Version: 6.9.2

Kernel Version: [output of uname -r]

Mesa Version: [if applicable]

HARDWARE
RAM: Corsair Vengeance RGB RT, DDR4, 32 GB (2 x 16 GB), 3600MHz, CL16

Motherboard: Gigabyte B550 AORUS ELITE AX V2 (Revision 1.5)

Fans: be quiet! Light Wings LX 140mm PWM High-Speed (3x front, 1x rear)

CPU: AMD Ryzen 7 5800X

CPU Cooler: Noctua NH-D15 G2 LBC

SSD Heatsink: be quiet! M.2 MC1 Pro

Drive: Samsung 990 Pro 1 TB

Case: Kolink Citadel Mesh ARGB (E-ATX compatible)

PSU: MSI MPG A850G PCIE5 850W

GPU: Gigabyte GeForce RTX 4070 WindForce OC 12GB

DAC: iFi Zen Dac V2 UPGRADED + iFi Audio iPower X (5V/3.0A) + iFi Audio iDefender+ + RICABLE MAGNUS USB HI-FI 3m USB-A → USB-B

Headphones: ISK HD 9999

Monitor: MSI G274QPX (1440p, 27", 240 Hz)

Keyboard: Endorfy Omnis Onyx White Kailh Red RGB

Mouse: Razer Basilisk V3

Microphone: HyperX QuadCast

ADDITIONAL INFORMATION
The issue occurs in all tested games.

I created a thread about this on Reddit, and other users confirmed they are experiencing the same problem.

Problem did not occur in KDE 6.4.4.

Using Wayland session with NVIDIA open‑source driver 580.82.09.