Can a healthy but very old MBP (5,5) with 10.6 OS be configured to operate on a Mesh wifi network?

To augment the other replies, no one likes to keep Macs in service more than I do, and in fact I have an iMac a litte older than that MBP. I'm using it now. It runs El Capitan, and is as fast as it's ever been.

However... its version of Safari is just too old to cope with most websites. So, on this Mac I use use Firefox almost exclusively since it is much newer than Safari for El Cap, and still works with every website I can think of:

But then it gets worse. Mozilla recently stopped supporting those older OS X versions, so it has already arrived at a dead end.

Even worse. Its version of Mail stopped being able to communicate with Microsoft Exchange email servers a long time ago. Even iCloud Mail stopped functioning as recently as a few weeks ago. That leaves very few options for using Mail, and I'm not even certain I can suggest any.

Summary: No, there are no fatal show-stoppers, but in my opinion it's just not worth trying to squeeze any more life out of that Mac. Yes you can make it work, but your old friend is almost certain to encounter many frustrations that will only get worse.

Options: You can buy a recently manufactured certified refurbished MacBook Air from Apple for considerably less than $700: https://www.apple.com/shop/refurbished/mac/imac-macbook-air

I'd seriously consider that.

if your MacOS is working, another way to proceed is you CAN use this article (fight your way through "this is not secure, bla, bla, bla") and get to the "Use a browser" direct download link for 10.11 El Capitan, which does not require an encrypted connection.

How to download and install macOS - Apple Support

Once downloaded, when you click through everything, a dmg provides a pkg, which will eventually PLACE the "Install macOS..." in the Applications folder, READY to be installed. The actual installation is a separate operation.

A MacBook Pro5,5 can connect to WPA2 secured networks, even running 10.6. But you say you have a home mesh network - are you sure it isn't using WPA3 security? 10.6 cannot connect to a WPA3 network (but if you can upgrade to 10.11 El Capitan as Grant Bennet-Alder suggests, then you can because 10.11 can properly fall back to WPA2 on a WPA3 network).

When you go to join a network, you should get a dialog like this (except the name of the network will be filled in):

When you click on the Security selector, you should get a drop-down menu like this:

Do you get this and can you select WPA2 Personal?

from there, you click on the lock, examine the certificate, and say "connect anyway"

but what you already know is that it can "Go Fishing" on the internet, and CAN discover stuff (it knows the site asked for a httpS: connection) but may not yet have adequate DNS numbers entered:

the numbers showing are OpenDNS, which are free to use and VERY reliable.

that appears to be a 2009 model with a built-in Ethernet port. It accepts up to 8GB of RAM and is capable of running up to MacOS 10.11 El Capitan. You can arm-wave the Wi-Fi issues by plugging in an Ethernet cable to any one of your many access points.

If it has a working MacOS, DO NOT Erase it unless/until you have another way of installing MacOS -- That computer does NOT have Recovery tools in its ROM.

it should be upgraded to MacOS 10.11 El Capitan to be able to see any modern web sites, and we can talk about how to do that.

What is the EXACT status showing in System Preferences > Networks > Wi-FI ?

In 2015, researchers discovered that Secure Socket Layer (SSL) Internet encryption was not nearly as secure as was thought, and needed to be replaced. Internet encryption quickly moved to Transport Layer Security (TLS) which was rapidly deployed across the Internet. Over time, sites tightened requirements for what was acceptable for encryption.

Apple issued Safari version 9 in 10.11 El Capitan version of MacOS, which included TLS encryption. It was later provided by Security Update into the two previous versions of MacOS. 10.10 Yosemite and 10.9 Mavericks, PROVIDED you applied all available software updates.

MacOS versions older than those can not make a lot of secure [httpS:] connections on the Internet, because by todays standards, your proffered SSL encryption is considered inadequate.

that Mac:

https://everymac.com/systems/apple/macbook_pro/specs/macbook-pro-core-2-duo-2.26-aluminum-13-mid-2009-sd-firewire-800-unibody-specs.html

I've installed 10.6 on a MacBook Pro4,1 and connected it to an eero mesh (but had to downgrade the eero security to WPA2, from WPA3, in the eero App under Network Settings by turning WPA3 off). Did it within the past 3 months, so it should be possible.

Get on the Internet through ethernet if you can, get Firefox and then update the OS to El Capitan. You may have to do this through the Terminal, running the following multiple times:

sudo softwareupdate -ia

Terminal is likely required because the App Store won't connect properly. Running sudo (super user do) will also require that you enter your password.

<< AirPort is Connected. >>

then the issue is NOT WP-anything -- you CAN Connect if its shows connected.

the most frequent problem once 'connected' is Domain Name Server address (DNS).

Launch a browser and enter this easy to remember all-numeric IP address:

1.1.1.1 

in the address bar,  and press return.

If you get the CloudFlare** splash page, your internet is working, but DNS lookup may not be working.

**CloudFlare is NOT part of the solution, they just own the easiest to remember all-numeric IP Address.

I think this is a probelm particular to Mac OS X and Safari with expired root certificates. You could try this:

Navigate to Let's Encrypt: https://letsencrypt.org/certificates/

Under ISRG Root X1, click the link that says "pem" after Certificate details (self-signed), to download that format root certificate.

Double-click the downloaded file to load it into KeyChain.

Or, you could try Firefox 45 ESR: https://ftp.mozilla.org/pub/firefox/releases/45.9.0esr/mac/en-US/Firefox%2045.9.0esr.dmg. which might still work enough to get you in a position to update.

g_wolfam

I agree that the certificates may be expired, but you should be able to 'show certificate' and then 'connect anyway'. It may read you the RIOT ACT about how this is not secure, but there should be a way to do that.

Your error message already told you that you ARE on the internet, and trying to access httpS: web sites.

Unless/until you fix certificate's,-OR- click on the lock, view the certificate, and tell it to 'connect anyway', adding DNS numbers is not expected to change 1.1.1.1 lookup.

but what it will do is allow other lookups that do NOT require httpS:

this is one I can remember:

time.is

it does not require a valid certificate. Just type that string into the search bar and it surfs (after a DNS lookup) to a web site that will tell you whether your system time is accurate. if your DNS is working, you will get there regardless of certificates.