Apricorn external HDD not showing on my M3 iMac

If you're using a different cable to connect it to the M3 iMac (which has USB-C ports) than to your other machines (which might have USB-A ones), check that the cable is rated to carry data.

There are USB-C charging cables that do not support data transmission at all. Seeing a portable drive or iPhone receive power, but not have any luck connecting to a Mac, is a classic symptom of using such a cable.

How is it connected to your M3?

Have you tried a different cable, port?

Have you installed and run any "cleaning", "optimizing", "speed-up", anti-virus or VPN apps on your Mac?

What I would do then is to give this as feedback to apple so that they can look into it. On these forums apple is not actively participating, we are apple users trying to help each other. If you want to give some feedback, do so using this link: Product Feedback - Apple

Even when those types of files are not running they have components running in the background.

First, there is no reason to ever install or run any 3rd party "cleaning", "optimizing", "speed-up", anti-virus, VPN or security apps on your Mac.  This documents describe what you need to know and do in order to protect your Mac: Effective defenses against malware and other threats - Apple Community and Recognize and avoid phishing messages, phony support calls, and other scams - Apple Support.  

There are no known viruses, i.e. self propagating, for Macs.  There are, however, adware and malware which require the user to install although unwittingly most of the time thru sneaky links, etc.   

Anti Virus developers try to group all types as viruses into their ad campaigns of fear.  They do a poor job of the detecting and isolating the adware and malware.  Since there are no viruses these apps use up a lot of system resources searching for what is non-existent and adversely affect system and app performance.

There is one app, Malwarebytes, which was developed by a long time contributor to these forums and a highly respected member of the computer security community, that is designed solely to seek out adware and known malware and remove it.  The free version is more than adequate for most users.  

Unless you're using a true VPN tunnel, such as between you and your employer's, school's or bank's servers, they provide false security from a privacy standpoint.  Read these two articles: Public VPN's are anything but private and Security Risks: The Dangers of Using Free VPNs (eccu.edu)

Uninstall the Bitdefender software according to the developer's instructions. Then Yyou can check to see if you've removed all of the supporting files by downloading and running the shareware app Find Any File to search for any files with the application's or the developer's name in the file name.  For the Bitdefender software you'd do the following search(es): 

1 - Name contains bitdefender

Any files that are found can be dragged from the search results window to the Desktop or Trash bin in the Dock for deletion.

FAF can search areas that Spotlight can't like invisible folders, system folders and packages.  

If you get warnings that the file can't be deleted because it is in use or used by another app boot into Safe Mode according to How to use safe mode on your Mac and delete from there.

Note:  if you have a wireless keyboard with rechargeable batteries connect it with its charging cable before booting into Safe Mode.  This makes it act as a wired keyboard as will assure a successful boot into Safe Mode.

The test again to see if the problem persists.

You can try and format it in to macOS journaled to see if the issues persist, but then you cannot use it with your windows pc anymore

Hmm very weird, as the Apri corn used to be cross-platform. Have you tried to use it in AFPS?

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