Why is my WD Elements drive not mounting?

You may have installed Western Digital drive software in Yosemite when you first began using this WD Elements drive. That software is now likely incompatible with Mojave, and is preventing your NTFS formatted drive from mounting. I recommend downloading and running EtreCheck (completely safe) that will provide a detailed report of what is installed in System locations that may be contributing to the problem. Copy the EtreCheck report to your clipboard, click the indicated button in this editor, and paste the EtreCheck report there. Then we have something to talk about. Give EtreCheck full drive access for a more detailed report.

See these two articles:

reset SMC - https://support.apple.com/en-us/HT201295

reset NVRAM - http://support.apple.com/en-us/HT204063

The OS upgrade itself shouldnt have anything to do with it but during the upgrade process some electrons might have gotten twisted around. Try the SMC reset first.

If it were me, and looking at all of the outdated software that you have installed on this machine, I would perform one last backup, print out the EtreCheck report for reference, and then perform a clean install. It would take me a week to pour over all this stuff and make recommendations.

Re=introduce only the 64-bit, third-party software updates that you actually plan to use. None of those existing 44 32-bit applications will work on Catalina, so don’t upgrade until you address that issue. You can see most of these in the System Information : Software : Legacy Applications panel. Some 64-bit applications may have internal 32-bit helper applications and these may/may not appear in that listing.

Otherwise, there are too many potential collisions between anti-virus (AVG) software, outdated software packages, and old third-party kernel extensions to specifically state the cause blocking the mount of that external NTFS drive.

You are about out of drive space on the boot SSD, and you are running far too many concurrent applications for your 8GB RAM, so you are swapping to the SSD and the Mac is crawling when that occurs. Free up storage now. Visit System Preferences : Users & Groups, and remove everything from the Login Items panel. That will free up some valuable RAM too.

You are running an anti-virus (AVG) tool that is likely introducing a number of intrusions of its own on normal System operating behavior, and steeling RAM. It cannot find any viruses because they simply do not exist on the Mac. I Highly recommend that you uninstall AVG per vendor’s instructions, as it could just be the single problem preventing that external drive mount. See if there is a menu item in the AVG application that offers to uninstall it.

The third-party TRIM Enabler software is likely way out of date. There is built-in ability to use Apple’s own TRIM from the command line that may enable TRIM on the EVO, or it may have built-in TRIM in its controller. This outdated third-party TRIM enabler may also be a contributing collision with the Paragon NTFS drivers.

It is a safe bet that all of your Internet-plugins are now incompatible with Safari 12 and later.

You are welcome.