MaBook Pro with macOS Ventura 13.7.6 Keep finding errors but seems to repair so

You have to do it in Recovery mode.

There are simply too many unknowns to provide an accurate answer, but given your concerns the first order of business is to create that Time Machine backup. Preferably, more than just one. Then, you will have options.

We have no access to passwords stored locally on the startup device when booted in Recovery mode, but "first aid" will not erase them... unless of course it's malfunctioning, and you already determined the startup device has corruption that needs to be fixed.

It should go without saying, do nothing without a backup. If you do not back up your Mac, by definition you have no concern for its contents. To learn how to use Time Machine please read Back up your files with Time Machine on Mac - Apple Support. Personally I do nothing without at least two separate and redundant backups. All the Macs I care about have at least three, but everyone's backup needs are different.

(I remember saving things but also redefining them)

If you saved them and subsequently changed them, whatever you saved is no longer valid. That seems obvious to me though, so am I misunderstanding something?

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