old 2006 Mac security has lapsed and can't use eBay or any shop platform

I'm surprised that your neighbor has not run into problems browsing the Web long before now.

The original form of https security was found to be insecure, and there was a concerted move to upgrade Web sites and browsers to use a stronger protocol. Modern https Web sites are likely to reject connections from any browser that only knows how to connect using the old protocol.

A 2006 iMac cannot run anything later than Snow Leopard (early/mid 2006 models) or Lion (late 2006 models).

The change to upgrade Safari to use the new security protocols first went into El Capitan, and I don't believe that it was ever back-ported to Snow Leopard or Lion.

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Another problem with using such old operating systems, and old versions of browsers, is that sites have evolved in other ways not directly related to security. An old browser may not be able to render pages from current Web sites well enough for those pages to be useful.

1. No
2. It is not real, which obviates the remainder of your questions except for:

Any other ways to update or solve this problem?

No browsers that can be installed and run on that Mac can be used for any recent websites requiring recent security protocols. Stated differently yes the Internet will work, but most websites won't. Most email services won't work either.

Websites that do not use encryption will load, such as http://www.gremlinx.com which illustrates the effective age of that Mac.

Unfortunately, modern internet requirements have forced the retirement of old computers, in terms of both secure and practical usage. For online business and financial transactions, continued use is too risky. It's a tough pill to swallow, but a computer that's almost 20-years-old has more than paid for itself.

As far as your friend having "the latest version" of Firefox, he is mistaken. The extended support release of Firefox 115 is intended for older Macs running Mac OS 10.12 - 10.14. Since every 2006 model iMac can't be updated to those OS versions, there is no supported version of Firefox that your friend can run.

From the Mozilla website:

The online Apple Store has a Certified Refurbished section.

Since we seem to be discussing desktops, I set the filter on this link to iMacs and Mac minis, but you can change it if you want to see other models (like MacBook Airs).

Apple – Certified Refurbished Macs

Typically, Certified Refurbished prices are 15% off original list, which may or may not be a good deal depending on whether you can get the configuration you want, and how older products compare to current ones. But the quality of the refurbishment process is very high, you get all accessories and cables (e.g., ,the keyboard and mouse in the case of an iMac), you get a one-year warranty (and the chance to buy AppleCare+), and you get free shipping.

When he first bought that Mac may seem like yesterday to him but he got couple of decades out of it. That's pretty good and a testament to how long Macs last in general. They are the least expensive computers to own, by far.

If the Mac were only ten years old, sure, it would still be usable. 19 years old... no. Buy him a new or refurbished Mac, and he'll get another decade out of that one.

I think it's great that someone in his 90s uses a computer for online shopping. If cost is a factor when considering the purchase of a new computer, do you know if there are any computer resellers in your area that carry used, Apple computers? Hopefully, he could find one that's a lot newer than his 20-year-old iMac, affordably-priced, and running an OS version that supports modern browsers. He probably would prefer an all-in-one model like an iMac, to eliminate the purchase of a separate display. A limited warranty of some duration, even 90 days, would be important, just in case there's a problem. Most legitimate resellers warrant the products that they sell. That would enable him to give it a good workout and be sure that it's fully-functional. Buying a used computer online involves the shipping expense, which most would prefer to avoid.

Other World Computing is another source of used Macs.

Other World Computing – New & Used Macs

Their warranties on used Macs are normally only 90 days, and the warranties are OWC ones, not Apple ones.

They carry some very old Macs – such as an 21.5" Late 2013 iMac with 8 GB of RAM and a 1 TB mechanical hard drive for $49. That one cannot run anything later than Catalina – which is just enough to run the current version of Firefox, but not enough to run current versions of any other major Web browser. And the $49 doesn't include the keyboard or mouse (that come with new and Apple Certified Refurbished iMacs), or shipping.

So selecting a Mac by cheapest price here – as elsewhere – might not be the best way to find out that supports modern browsers and that will continue to support them for a few years longer. But if you do your homework, as to what to look for, I would certainly trust used Macs from OWC much more than used Macs being sold by some random seller on an "electronic marketplace".

Servant of Cats wrote:

Other World Computing is another source of used Macs.

+1 👍 Just want to add that I have had great success with all the used Macs and other products that I have purchased from OWC. Every one has been in great condition and I have had no problems with any of them.

FWIW, I also purchased OWC's Eclipse warranty for each Mac ... and haven't had any reason to use it. At present, OWC is offering 1-year Eclipse warranties free and the 2-year warranty on an iMac is only $40.