The official way to do this is first creating a new steam library on the new hard drive, then under the property page of each game you find an option to move the game to a new library.

You could've figured this out by just right clicking on any random game, selecting "properties", and observing what kind of options you get.

Once you have created more then one Steam Library in the Steam Settings, each install will ask you which Drive (Library) you wish to install it to.

If you have alot of games on an old drive and you want those on the new drive, the easiest and fastest way would be to simply do an entire disk clone. Once cloned, remove the drive letter from old drive and set new drive to drive letter of the old drive. Then set old drive to something else, then format old drive.

There is no "official" way. The way I do it is the way it's worked for anyone who uses my method since Steam has existed.

If you have more specific / direct questions, feel free to ask.

Just to add this too if anyone doesn’t know yet:

One of the best things about Steam is also that if you remove your SSD/hard drive which you game is installed on, and put it in another computer and login into your account, you just need to add that drive in the settings and play your games without needing to redownload anything. When my PC died a few weeks ago I was desperate to play games and just took my game drive to my friends computer and logged in on my account and played them without any downloading. Steam is best!

Yes even if you go and part out a current Steam library and Steam at first seeing game as not installed, this is due to missing or incorrect manifest app data, simply point tye install to the drive + library where the game now exists and it will see it, verify it and not have to redownload it. EA and UBI work the same way

Thank you very much to everyone who has responded to this thread.
From the Settings in the Storage tab it gives you the option to add another hard drive and do the transfer via Steam.
I am currently doing the transfer of games via Steam. Once I'm done and have results I'll come back with what and if it was done correctly.

The steam method, that transfer method is one game at a time. You can just go copy the entire library or game from one drive to another as long as you understand the folder structures and understand that ifa library is manually copied from one drive to another you'll have to then exit Steam and rename it, then launch Steam and add a library on that new drive, once done exit Steam once more and delete the library it created which is juat empty folder at this point and then rename old library as the same name. Then Steam will pick that up ob next launch and games not showing as installed simply click install and select this new library and then the game gets verified.

Much easier this way when you want to copy over a bunch of games. Yes the verify still have to be done but that's not important until you would go to actually play that game