Why am I having a severe mouse lag when CPU usage spikes up to %100?

To capture the CPU usage in Windows 10, open cmd.exe as admin and run wpr.exe -start CPU -start ReferenceSet -filemode && timeout -1 && wpr.exe -stop C:\HighCPUUsage.etl and when you captured 30-60s of the lags press a key to stop the logging.

Now load the generated C:\HighCPUUsage.etl in WPA.exe (You need to install the Windows Performance Toolkit from the Windows 10 SDK) by doing a double click on it.

Drag & drop the graph CPU Usage (Sampled) from the left side under Computation to the Analysis pane

and change the view to DPC and ISR Usage

Configure and load debug symbols in WPA.exe and extand the stack of ntoskrnl.exe and under ntoskrnl.exe!KiExecuteAllDpcs I see calls of sshid.sys and other Microsoft Mouse/keyboard drivers. sshid.sys also seams to be a mouse/keyboard driver. so update the driver or use the default MS drivers which provide only basic features.

While executing DPCs the whole system is blocked and this could cause your lags.

just sharing my experience as I searched multiple forums about this topic.

For me, this definitively solved the issue : deactivating startup load of every instance of "RtkAudUService64.exe", until there is no more any instance of it in the Task Manager after reboot.