It’s not clear if this is a hard disk drive failure. That’s why I’d suggested the bootable diagnostics, and—if the diagnostics show storage errors—testing with booting from external storage.
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This could well be caused by something else, so swapping parts is a little early.
A failure of a decade old hard disk would not be a surprise.
Hard disk drive failures—again, if that is actually what is causing this misbehavior—tend to start with pauses and slowdowns and beachballs, and then progresses to hangs and crashes and corruptions, and to complete failure.
There’s usually no pattern to what apps are involved with a storage failure—or a memory error, for that matter—as that’s entirely dependent on what apps and data are effected by the particular failure.
SMART data is less than entirely reliable, and less than entirely predictive of failures. And diagnostic tools also don’t always find errors, particularly transient errors.
EtreCheck can also sometimes show storage failures. Download and run that and share the results to the clipboard, then open a new reply here and press the button that looks like a printed page (additional text, text attachment) to get a text input box big enough to paste the hardware and software configuration report here.
Have backups of any important data. Always. Particularly now.
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