Does anyone know how to decrypt TM without doing Erase-Format in Disk Utility?

Running Mojave 10.14.5 on 21.5" iMac (late 2015). I have a 2TB external hard drive partitioned into two 1TB partitions. One of the partitions is dedicated to Time Machine, the other is just a Static backup of files that I do not keep on the Mac. Both partitions were formatted as "extended, journaled, encrypted" using Disk Utility. I know how to decrypt the Static partition using Finder, Control and Click on the drive and then select decrypt. But, there is no Decrypt option when using that method for the Time Machine partition. Even if you remove that drive from Time Machine you can not decrypt using Finder.

Does anyone know how to decrypt TM without doing Erase-Format in Disk Utility?