I forget the name, but there is a utility I used to use that would run a brute force test on a hard drive, the sort of test you run overnight like MEMTEST for checking RAM. It may be a Western Digital Utility. I'll see if I can find it. The reason I've forgotten is that my WD drives have been very reliable in the last decade, but problems can happen.

Check your drive temperature. Get a utility like Speccy. If a drive's performance is intermittent like you describe, that might be it on a summer day. If the temp is running high, check the cooling fans for dust.

Another basic test: did you rule out malware? That can make you tear out hair trying to isolate problems that aren't even hardware. Run Malwarebytes to start.

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