Thanks to the polygon annotation tools, it is easy to create a Field Boundaries:
Step 1: Draw an annotation which represents the field boundaries
Step 2: Click on the annotation which appears on the layer panel. This will display the info panel on the right
Step 3: Click on the 3 dots close to annotation name
Step 4: Choose "Convert to - Field boundaries"
Step 5: The annotation is now converted into field boundaries and appears under "contours"