Hi there,
For most people, the high memory usage caused by Antimalware Service Executable typically happens when Windows Defender is running a full scan. We can remedy this by scheduling the scans to take place at a time when you're less likely to feel the drain on your CPU.
If the High CPU is not during the scan then you can try running the SFC & DISM scan to sort this out
https://support.microsoft.com/en-us/windows/using-system-file-checker-in-windows-365e0031-36b1-6031-f804-8fd86e0ef4ca
I would also suggest you to create a new account on your PC and check if you have same memory usage as the corrupted user profile might also cause this issue.
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