Just built a completely new bed and covered the soil with cardboard and 75-100mm of home made compost will this be ok for kale and cabbage as I read they need firm soil?
For all new beds in summer, you need to firm the compost, as I show in my video where I walk on it.
I wonder if you needed the cardboard, unless there are perennial weeds.
Plant brassicas deep in the firm compost, and they will be fine.