Window previews aren't updating, outside certain circumstances

System:    Kernel: 5.7.12-1-MANJARO x86_64 bits: 64 compiler: gcc v: 10.1.0 
           parameters: BOOT_IMAGE=/boot/vmlinuz-5.7-x86_64 root=UUID=c28c9ba1-1ab9-48ed-a6c3-a5cf6794acea rw quiet apparmor=1 
           security=apparmor udev.log_priority=3 
           Desktop: KDE Plasma 5.19.4 tk: Qt 5.15.0 wm: kwin_x11 dm: SDDM Distro: Manjaro Linux 
Machine:   Type: Desktop Mobo: Micro-Star model: B450M MORTAR MAX (MS-7B89) v: 1.0 serial: <filter> UEFI: American Megatrends 
           v: 2.70 date: 04/21/2020 
CPU:       Topology: 8-Core model: AMD Ryzen 7 2700X bits: 64 type: MT MCP arch: Zen+ family: 17 (23) model-id: 8 stepping: 2 
           microcode: 800820D L2 cache: 4096 KiB 
           flags: avx avx2 lm nx pae sse sse2 sse3 sse4_1 sse4_2 sse4a ssse3 svm bogomips: 118418 
           Speed: 1974 MHz min/max: 2200/3700 MHz boost: enabled Core speeds (MHz): 1: 2028 2: 2134 3: 2069 4: 2013 5: 2270 
           6: 2568 7: 2139 8: 2144 9: 2118 10: 2039 11: 2739 12: 2665 13: 2169 14: 2171 15: 1951 16: 2189 
           Vulnerabilities: Type: itlb_multihit status: Not affected 
           Type: l1tf status: Not affected 
           Type: mds status: Not affected 
           Type: meltdown status: Not affected 
           Type: spec_store_bypass mitigation: Speculative Store Bypass disabled via prctl and seccomp 
           Type: spectre_v1 mitigation: usercopy/swapgs barriers and __user pointer sanitization 
           Type: spectre_v2 mitigation: Full AMD retpoline, IBPB: conditional, STIBP: disabled, RSB filling 
           Type: srbds status: Not affected 
           Type: tsx_async_abort status: Not affected 
Graphics:  Device-1: NVIDIA GP102 [GeForce GTX 1080 Ti] vendor: ASUSTeK driver: nvidia v: 440.100 
           alternate: nouveau,nvidia_drm bus ID: 26:00.0 chip ID: 10de:1b06 
           Display: x11 server: X.Org 1.20.8 compositor: kwin_x11 driver: nvidia display ID: :0 screens: 1 
           Screen-1: 0 s-res: 2560x1440 s-dpi: 108 s-size: 602x342mm (23.7x13.5") s-diag: 692mm (27.3") 
           Monitor-1: DP-0 res: 2560x1440 hz: 144 dpi: 109 size: 597x336mm (23.5x13.2") diag: 685mm (27") 
           OpenGL: renderer: GeForce GTX 1080 Ti/PCIe/SSE2 v: 4.6.0 NVIDIA 440.100 direct render: Yes 
Audio:     Device-1: NVIDIA GP102 HDMI Audio vendor: ASUSTeK driver: snd_hda_intel v: kernel bus ID: 26:00.1 
           chip ID: 10de:10ef 
           Device-2: Advanced Micro Devices [AMD] Family 17h HD Audio vendor: Micro-Star MSI driver: snd_hda_intel v: kernel 
           bus ID: 28:00.3 chip ID: 1022:1457 
           Device-3: GYROCOM C&C UAC1 DAC type: USB driver: hid-generic,snd-usb-audio,usbhid bus ID: 1-10:2 chip ID: 1852:5110 
           Sound Server: ALSA v: k5.7.12-1-MANJARO 
Network:   Device-1: Realtek RTL8111/8168/8411 PCI Express Gigabit Ethernet vendor: Micro-Star MSI driver: r8169 v: kernel 
           port: e000 bus ID: 22:00.0 chip ID: 10ec:8168 
           IF: enp34s0 state: up speed: 1000 Mbps duplex: full mac: <filter> 
Drives:    Local Storage: total: 1.18 TiB used: 351.41 GiB (29.0%) 
           SMART Message: Unable to run smartctl. Root privileges required. 
           ID-1: /dev/sda vendor: Samsung model: SSD 860 EVO 500GB size: 465.76 GiB block size: physical: 512 B logical: 512 B 
           speed: 6.0 Gb/s serial: <filter> rev: 4B6Q scheme: GPT 
           ID-2: /dev/sdb model: SSD 910 200GB size: 186.31 GiB block size: physical: 4096 B logical: 512 B serial: N/A 
           rev: a424 
           ID-3: /dev/sdc model: SSD 910 200GB size: 186.31 GiB block size: physical: 4096 B logical: 512 B serial: N/A 
           rev: a424 
           ID-4: /dev/sdd model: SSD 910 200GB size: 186.31 GiB block size: physical: 4096 B logical: 512 B serial: N/A 
           rev: a424 
           ID-5: /dev/sde model: SSD 910 200GB size: 186.31 GiB block size: physical: 4096 B logical: 512 B serial: N/A 
           rev: a424 
RAID:      Supported md-raid types: raid0 
           Device-1: md0 type: mdraid status: active Components: online: sdd~c3 sdb~c0 sdc~c2 sde~c1 
           Info: raid: raid-0 blocks: 780914688 report: N/A chunk size: 512k super blocks: 1.2 
Partition: ID-1: / raw size: 465.26 GiB size: 456.96 GiB (98.22%) used: 191.49 GiB (41.9%) fs: ext4 dev: /dev/sda2 
Swap:      Kernel: swappiness: 20 (default 60) cache pressure: 100 (default) 
           ID-1: swap-1 type: file size: 500.0 MiB used: 0 KiB (0.0%) priority: -2 file: /mnt/faaast/swappy 
Sensors:   System Temperatures: cpu: 49.9 C mobo: 44.0 C gpu: nvidia temp: 47 C 
           Fan Speeds (RPM): fan-1: 0 fan-2: 1339 fan-3: 932 fan-4: 755 fan-5: 974 gpu: nvidia fan: 41% 
Info:      Processes: 315 Uptime: 21h 21m Memory: 31.38 GiB used: 4.04 GiB (12.9%) Init: systemd v: 245 Compilers: gcc: 10.1.0 
           Packages: pacman: 1326 lib: 389 flatpak: 0 Shell: Bash v: 5.0.18 running in: yakuake inxi: 3.1.05

I have a weird issue, where the window preview (or tooltip) doesn't update in real time, when there's something like a video playing on it. But if I keep moving the mouse over the preview in a constant motion, it does keep up with the playback, instead of being a slideshow, or just a still image.
Also, if I have like two separate Firefox windows open, and both are playing a video, both previews are updated on their own...
This seems like some kind of acceleration limiter to me.
And it's not exclusive to Firefox. Previews are like this for mpv as well.

P.S. It's been like this ever since I moved from Windows to Manjaro in early June; this issue wasn't introduced in a recent update.

Task Manager uses a way to display the tooltips of playing videos windows.
Icons-only Task Manager uses a different way to display the tooltips of playing videos.
Latte-Dock has a different code to show these previews. It doesn't fail.

No relation or corelation between one and another.
KDE Plasma developers need to address this in a way or another.

Meaning I've had the issue from day one, since ditching Windows for Linux. Not that Windows has anything to do with this issue.

But good to know it's probably not a misconfiguration in my part.

You can check if you have the video-linux installed and remove it. Sometimes the nvidia.conf by default is not enough on some systems and some tweaks can be done there too, and also for kwin as described here:

Using Latte-Dock instead of the default Panel seems to be a thing this days, maybe worth investigating that too.

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