This might be worth trying. First created a temporary new linestring layer. This is for guide purposes only and can be deleted after the main digitising is complete.
Quickly (accurately!) draw a line along where you want to avoid. By the look of your image that would be the road verge (blue line). Then under Style of the layer properties add a new simple line and change the Symbol Layer Type to 'Geometry generator'. Set Geometry Type to 'Linestring/MultiLineString'. In the expression box write:
The second line is now offset by so much either to the left or right. When I did this on my computer using OSGB1936 coordinate system, the line was offset to ~5m (+- 0.1m).(I'm guessing this could get complicated if not using meters but I wouldn't know personally).
I repeated the previous step to create another two lines with this as the expression:
This offsets two lines at 10m and 20m.
If these line are created on the wrong side then just change them to negative numbers and the lines will be generated on the other side of your original.
You won't be able to snap to these lines but it'll give a good enough guide to digitize against.
The buffers in the image were also created using the geometry generator so I could get a decent guide (