Just for my own reference, this seems to work:
To stop Citrix from automatically starting up the file that needs to be (re)moved is called com.citrix.ReceiverHelper.plist (Located in the protected folder /Library/LaunchAgents)
To do this safely you need to move it to another location where it won’t be looked at during startup. It can probably be deleted but to keep things safe I would suggest putting it into your downloads folder.
The commands below can be copied and pasted if you want.
To disable citrix from auto-Starting:
Start Spotlight by pressing command-space and type in terminal
In the terminal app type the following command:
sudo mv /Library/LaunchAgents/com.citrix.ReceiverHelper.plist ~/Downloads
You will need to enter your password (I’m assuming you are an admin for your Mac) as the ability to set or remove a launch agent is priviliged.
To undo this:
You can undo this at any time by moving it back with the reverse command:
sudo mv ~/Downloads/com.citrix.ReceiverHelper.plist /Library/LaunchAgents/
Or you could probably just reinstall citrix.