Merging APFS Containers using the Disk Utility Application I recently deleted my dual boot from my mac, but I am now left with two partitions that I can't figure out how to merge. I would like it to be normal again with just one container: Macintosh HD. I'm running MacOS Mojave.

Here is my current situation as shown in the "Disk Utility" application and the output from the diskutil list command.
If you wish to do this in the GUI, you can do advanced hard disk editing with Paragon Hard Disk Manager.
Not "merge" merging the containers, but most likely you'll need to remove a containter and then resize main container where the macOS resides. It can be done on the fly - i.e. you can edit the same partition/container from which you booted the system. Paragon Hard Disk Manager has 10 day trial period, during which you can use all its functions.