Can't mount or format external drive with APFS volume

You need to erase the physical drive instead of the Container.

Beginning with macOS 10.13 the physical drives are hidden from view by default within the Disk Utility GUI interface. So with Disk Utility you need to click "View" and select "Show All Devices" so that the physical drives appear on the left pane of Disk Utility. If you still cannot erase the drive when selecting the physical drive, then write zeroes to the beginning of the physical drive using "dd" so that the partition table and early part of the file system is overwritten. Sometimes Disk Utility just cannot handle drives which may have unexpected or corrupted layouts. Usually I only have to do this with external drives especially USB sticks especially ones where I "burn" an ISO file to it.

It is also possible the physical drive may be failing. You can try running the Apple Diagnostics to see if any hardware issues are detected, however, the diagnostics don't detect a lot of drive failures so this is only useful if the diagnostics fail. If you can boot an external macOS drive, then you can check the health of the internal drive by running DriveDx and posting the report here using the "Additional Text" icon which looks like a piece of paper. DriveDx does a good job interpreting the health of a hard drive, but can give false failures when interpreting the health of an SSD. If you have a non-USB-C Mac, then I can provide instructions for checking the health of the drive using a bootable Linux USB stick if you are interested.

Edit: I forgot you mentioned external drive so you can use DriveDx, but it will require installing a special USB driver in order to access the health information of the drive over USB. However, even with the special USB driver some external drives won't allow access to the health information on the external drive.

You may also want to try using another USB cable. Also connect the external drive directly to the laptop as any adapters, docks, and hubs may be causing problems. If you must use an adapter, then try using another one especially a different brand. Also try using other ports especially on the other side of the laptop.