My MacBook is being remotely accessed / hacked repeatedly

Your Mac has been set to start in "verbose mode" (not Single User mode, which is different): Ways to start up your Mac - Apple Support

Resetting NVRAM to defaults is the easiest way to fix it: Reset NVRAM or PRAM on Mac - Apple Support

... my MacBook is being constantly accessed remotely by a user.

I didn't address that question, but more information is required, a lot more. I suggest addressing the "verbose mode" problem first, then describe the reason you believe your Mac has been subject to malicious interference. That's a serious concern.

You should not have duplicated Data drives.

You need to reformat (erase) the drive using the recovery process and have a true clean install.

https://support.apple.com/en-us/HT204904

Whoever did your "clean install" spectacularly failed.

If there is a prompt to type in, type reboot and hit return

It's not a hack. Your Mac is, for whatever reason, starting up into Single User Mode.

Unless you actually install Linux onto a separate partition of the drive, you cannot run any Linux apps. macOS is built on top of Unix. While they look much alike, Unix and Linux are anything but the same.

I'm not great at reading these messages, so I'm not sure why the Mac is bombing out to the command line.

It’s going on verbose mode for some reason back up your data on a external hard drive or online like onedrive then reboot to factory settings I hope I helped

Catalina creates two Mac HD volumes: the first is read only and contains your OS and system; the second (Mac HD - Data) contains your User folder and apps and is read/write. You have two Mac HD Data volumes because you did not follow a certain protocol; the new APFS file system will create a duplicate of your Data volume every time you reinstall (without following the protocol) - which is outlined in this Apple article:

https://support.apple.com/en-us/HT208496

It's normal for the command prompt to reappear. Restart your Mac.

ss242 wrote:

It won't let me do the reset. It won't shut down correctly... it's almost like it's not shutting down. Is there another way to do this? When I first came across this problem, somehow a guest user was created on my Mac with admin privileges and file sharing was on for everything. I've never let anyone else use my Mac before and never allowed guest privileges.

Setting aside for the moment the grave concern about using a Mac that has almost certainly been subjected to malicious tampering, you can reset NVRAM from the command line in Terminal:

sudo nvram boot-args=""

... should reset just the one that invokes the "verbose boot" mode.

Type your Admin password at the prompt. It won't be echoed, not even with •••• characters. Then press Return.