Question on a complete backup.

BUT, does it backup the OS as well?

No. If it is necessary, you reinstall the OS, then migrate your account from your Time Machine backup.

Is/are there any special setting to ensure I get a complete backup that includes the OS?

There are no settings because it cannot be done.

If you want to revert to a previous OS, make a bootable USB Installer of your current macOS and make sure you can boot from it. You will need that to reinstall that OS.

Create a bootable installer for macOS - Apple Support

If you have enough room on your drive, create an APFS Volume and install Sequoia into that volume and test. If all goes well, migrate your data into that volume and remove the Sonoma volumes.

Use more than one version of macOS on Mac - Apple Support

When you attach an external disk, macOS will prompt if you wish to make this a Time Machine drive. If you do it will be formatted and prepared to act as the Time Machine drive. Within about 15min Time Machine will backup every single file on your disk including all the Apple system files. Then it will incrementally backup files that are new or changed every hour. It rolls hourly into daily into weekly into monthly. If drive is not attached, macOS will snapshot the backups to the internal disk then move them to the Time Machine drive when it is online.

An excellent commercial alternative is CCC - Carbon Copy Cloner

Both Time Machine and CCC work in a similar fashion but CCC gives you some rather nice perks and more options.

Creating a backup is key to protect your Mac from a variety of catastrophic data loss scenarios:

When I installed SeaMonkey on Sequoia it failed to launch.

Turns out that error is related to the App not being properly notarized. Notarization is where devs submit their project to Apple who then scan it for malware or hidden malicious code then Apple signs it so it is trusted. This is done for Apps outside the AppStore. But to do this you need a paid Developer account at $99/yr and these community open source developers don't want to pay. They have no such requirements for Windows or Linux. They likely have a lot more Linux users than Mac users. They are volunteers working for free.

I was able to get SeaMonkey to launch by navigating to /Applications/SeaMonkey.app/Contents/MacOS/ and running each of the multiple binaries. The go to System Settings -> Privacy & Security, scroll down all the way and under Security there will be an Open Anyway button. Click it multiple times then run the binary again and it actually opened SeaMonkey. I haven't tested beyond that. But even then, the actual App icon doesn't work, still has the same error.

This tells me the dev's didn't test on betas and didn't build their app properly for macOS. It should not display that error. It is supposed to popup and say this App couldn't be checked for malware, etc. There's a cancel and Move to Trash when clicking the icon. At that point you click Cancel then go to Privacy & Security and Open Anyway and that should be all you need do. Lots of other open source apps work properly.

Looking at their forums and code repos, you aren't kidding about SeaMonkey having lots of problems. They have quite a few dev's working on SeaMonkey but maybe only a few who do the macOS version.

Maybe you are familiar with this error and know the workaround / fix. It's possible that it may occur on Sonoma as well.

There is no rush to upgrade to Sequoia. You can stay on Sonoma till it ages out of support. That means you are N-1 which is to say one release behind the latest macOS. I typically recommend users stick to the N-3 rule and run a macOS version that is no more than 3 versions behind the latest version and keep it updated.

Ralph6410 wrote:

I (actually my wife as a second user) have used Netscape's replacement Mozilla Sea Monkey as her email client. Years of emails, pictures etc are stored in that program. I know I should transfer “everything” to a more recent email program… (TB?) but at 79 change is hard for her. (As well I doubt my ability to transfer everything without messing up. I/we grew up with MS Windows, Apple operates in some strange/different ways, in my opinion.

Anyway, Sea Monkey has not played well with Apple in the past, and, as it is no longer as popular as it was… and even less used in an Apple environment, so problems are not often found/mentioned or fixed in a timely manner.

You might investigate exporting all the email from Sea Monkey to something that is better maintained. Doing some quick searching online, I found instructions for exporting Sea Monkey emails to eml format which can be imported into Apple Mail. Other instructions showed how to export to a format that MS-Outlook can import. Outlook and Apple Mail are maintained by Microsoft and Apple, two giants, I think they will keep their mail programs well supported.

What programs are you worried about? Have you checked for updates to these?

Take a look at Vivaldi 7 is has a lot of the same features as SeaMonkey.

https://tidbits.com/watchlist/vivaldi-7-0/

It has email built-in to the browser just like SeaMonkey.