"Turn Off FileVault" Button Grayed Out -- Seeking a Sure-Fire Solution

Friends, before you offer any suggestions, please read the following in its entirety, so you know what I have already tried. Thank you!

Well isn't this just grand! Here is the situation:

Even though I never use it, a short while ago, I turned on FileVault on my Mojave 10.14.3 2017 27" 5K iMac so that I could help out another fellow Mac user here.

After helping out this person, I went back to the FileVault prefs pane, entered my Admin password, and then went to click on the "Turn Off FileVault" button. According to the instructions which are found on this page . . .

https://support.apple.com/en-us/HT204837

. . . that is all that should be required in order to turn off FileVault. More specifically, it says the following:

Turn off FileVault

If you no longer want to encrypt your startup disk, you can turn off FileVault:

1. Choose Apple menu > System Preferences, then click Security & Privacy.

2. Click the FileVault tab.

3. Click Locked, then enter an administrator name and password.

4. Click Turn Off FileVault.

Hmmm . . . Right. Sorry Apple, but my "Turn Off FileVault" button is disabled/grayed out. :(

According to the progress bar, it still has at least 11 hours to go before the first disk encryption completes. Please don't tell me that I cannot disable FileVault until that occurs. If that is indeed the case -- which I don't believe it is -- then Apple should include something to that effect on the aforementioned page.

I came across one web page where a user had accidentally turned off FileVault while it was decrypting. He asked if he could turn it back on right away. The response he was given was that he had to wait for decryption to complete, before he could turn on FileVault again. I hope that doesn't work in reverse as well, meaning that I can't turn off FileVault until it has completed its first encryption.

Not happy with that possibility, I went searching for an answer. According to another thread I read, the following is suppose to work:

1. Boot my iMac in Recover Mode. [I did]

2. Launch Disk Utility. [I did]

3. Select the icon of the Volume where I want to shut off FileVault. [I did]

4. Click the unlock button in the toolbar.

[Huh? What unlock button? There is none. By "toolbar", I am not sure if this person means in Disk Utility's window, or the menubar at the top of my screen. In either case, there is no "unlock button" or any kind of lock icon in either place.

5. Select "Turn Off Encryption" under the "File" menu.

[Nope. There is no such option under the "File" menu, or under any other menu for that matter. In fact, I even held down the "Option" key and tried out the various menus again, in the hope that that sly option would suddenly and magically appear. Nope. No such dice.]

The only thing I could do -- which didn't help any -- was click on the "Mount/Unmount" button that is located on the end of Disk Utility's toolbar. Maybe that is what the person meant when they said "unlock button". If so, it was a poor choice of words. Let's be clear with our instructions please.

But even mounting the encrypting target volume did not help. There is still no "Turn Off FileVault" option under Disk Utility's "File" menu, or anywhere else.

Then I came upon another supposed way to turn off FileVault in the Terminal while in Recovery Mode. According to this method -- which again failed -- I did this:

1. Boot in Recovery Mode. [I did.]

2. Launch the Terminal app. [I did]

3. Enter the following command to get a list of UUIDs:

diskutil coreStorage list

[Nope. It didn't work. Instead, I got this: "No CoreStorage logical volume groups found".]

4. Unlock the drive using the following command:

diskutil corestorage revert UUID -stdinpassphrase

[Nope. I couldn't do it because I couldn't get the UUID for the volume from step 3.]

5. Enter your Admin password and decryption will begin.

[Nope. I couldn't even get that far due to failure at step 3 above.]

As a last resort, I disabled SIP and tried again, both from Recovery Mode while using Disk Utility, as well as in the FileVault preferences pane. Again, my efforts failed, and my internal drive is still busy encrypting.

So I am stymied. Is this what I get for trying to help out a fellow Mac user? Gosh.

So, I am open to suggestions folks; but please don't tell me that I have to do something drastic such as erase my hard drive and reinstall Mojave. That absolutely should not be necessary just to turn off FileVault on this machine.

Any takers?

Thanks in advance!