Connecting a Ext. Hard drive to older Mac

I misread “USB 4” to mean that you had two USB4/TB ports, not that you had 4 USB-A( USB 3 ) ones.

If that is a 27” iMac with model ID iMac15,1 then it is from Late 2014 or Early 2015. Its Thunderbolt ports would be Thunderbolt 2 ports with Mini DisplayPort connectors. Not USB4 ports (which have USB-C connectors and are new enough that they are found only on Apple Silicon Macs).

You couldn’t plug a USB-C( USB ) drive directly into one of those, even with a TB3-to-2 adapter. You’d need a TB dock to get anything to work.

So it looks like what you want is a USB-C to USB-A adapter so you can plug the drive into one of your four USB-A ports. Sorry for the confusion.

Question as I'm writing and make a correction on the prior text and save to seagate, will it substitute the changes in the text that has been recorded or will it just add a whole new recording?

I too write for income. I have two independent local backup drives, one doing Time Machine and the other making Carbon Copy Cloner bootable backups.

When you "save," that makes changes to the existing document, overwriting the old data. If you "save as..." and assign a new name—project231rev3; ...rev 4" etc—the older version is preserved.

Time Machine makes a backup every hour. If you know a change was made after a backup, you can find the older version with TM. The TM icon in your menubar tells you when the last backup was made:

However, I use DropBox for all in-process project files, most because I work on files from both my iMac and MacBook Pro notebook, and sometimes need to review from my iPad. That way I don't have to figure out the where the current version resides when I move fro one device to the other. You could also do that from iCloud drive.

It sounds like you have a M1 Mini, M2 Mini, or 24” M1 iMac. Assuming this is a USB-C drive but not a Thunderbolt one, you could plug it directly into one of the multi-purpose USB4/TB ports, or plug it into one of the USB-A ports with the aid of a USB-C to USB-A adapter (look for one rated for USB 3 speeds).

If this “hard drive” is actually a SSD, using a USB4 port might give you better speed. (E.g. if the drive is a SSD with USB 3.1 Gen 2).

Something like that should work, but I wouldn't get that particular one. If you "mouse over" the pictures to the left of the product description, one of the photos says "Stable and Fast Data Transfer. USB 2.0 up to 480 Mbps."

You want an adapter that supports at least USB 3.0 speeds, to avoid creating a bottleneck between your Mac and your new drive. Assume that any adapter whose description does NOT specify a "good speed" is a slow one. Here's one that claims to support USB 3.1 Gen 2 speeds (which is higher than your Mac supports), and thus would not be a bottleneck in the connection to your drive.

https://www.amazon.com/Monoprice-Adapter-Transfer-Compatible-Connection/dp/B07M981YYR/

If you save a new version of the file, it will overwrite and destroy the old version.

You can manually use “Save As,” or copying of files in the Finder, to keep some old versions around in case you want to look back through them.

If you use Time Machine to do “continuous” backups, it may save multiple versions of your documents, and offer a nice interface for browsing through them. However, Time Machine is not guaranteed to store all old versions.

What I might suggest is to use Time Machine but to also manually save snapshots of your book (under different file names) every now and then; especially before doing major rewrites.

Keep two or three backups of everything. Preferably, store one offsite except when updating it, so a fire or thief cannot take out ALL of your backups at the same time they take out your computer.

Disk space is cheap; lost work is expensive.