Hello NiallDooley,
Let's narrow this down and isolate it more by testing in safe mode and a new user account. Safe mode prevents certain software from opening and completes great checks on startup. More information on starting to safe mode and steps to take after starting there can be found in the link below after determining if you're using a Mac with Apple silicon or Intel chip.
How to use safe mode on your Mac - Apple Support
Apple silicon
1. Shut down your Mac.
2. Turn on your Mac and continue to press and hold the power button until you see the startup options window.
3. Select your startup disk, then press and hold the Shift key while clicking “Continue in Safe Mode”.
4. Log in to your Mac. You may be asked to log in again.
Intel processor
1. Turn on or restart your Mac, then immediately press and hold the Shift key as your Mac starts up.
2. Release the key when you see the login window, then log in to your Mac.
3. You may be asked to log in again. On either the first or second login window, you should see "Safe Boot" in the top right-hand corner of the window."
If the dock is still missing after following the steps from safe mode, create a new user account (administrator) to see if the behavior happens there. This will let us know if it is system-wide or something within your user account: Change Users & Groups settings on Mac
If you’re still experiencing the same issue, try the steps here: Use the Dock on Mac - Apple Support
Please let us know the outcome after giving the above steps a try.
Cheers!