While Atticus doesn't currently offer an option to turn off the automatic list numbering, there are a couple of workarounds you can use to achieve the desired formatting:
Copy and Paste: You can paste the 1. (including the space) into Atticus using the keyboard shortcut CTRL/CMD + Shift + V. This will paste the text without carrying over the automatic list numbering.
Out-of-Order Typing: Alternatively, you can type the number slightly out of order. For example, you could type the .(space) first, then go back and add the 1. This can help you avoid triggering the automatic list numbering.