safari can't open the page because safari can't establish a secure connection

First let's solve what can be solved. An inaccurate system clock will wreak all sorts of seemingly unrelated havoc: Set the date and time on your Mac - Apple Support. Set it manually if you have to. Confirm its time zone is also correct.

Since it appears your Mac doesn't know where it is, make sure Location Services is enabled: Allow apps to detect the location of your Mac - Apple Support. That should be sufficient for Date & Time to set your Mac's clock automatically.

If all those parameters are correct, your Mac should be able to run Catalina, so update or upgrade as required: Update macOS on Mac - Apple Support. Its version of Safari is recent enough for any website requiring secure connections.

Let me know if any of this helps resolve the problem.

It is possible the old Mac you want to give away is too old to run recent Safari versions, in which case the "can't establish a secure connection" message you see is not really surprising. Most websites today use security that very old versions of Safari are unable to cope with.

How old is this Mac?

I have tried several times to reset the clock but when I tick "set time zone automatically using current location" it never can determine current location at this time.

That can also cause the error you describe.

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I don't know why the time server field was empty, but you can specify any NTP time server you wish.

The default in the US is time.apple.com

There should be a dropdown menu that includes that selection, or you can just type it in manually.