The newly sown lawn is full of weeds

Hard to say. Can you take a close-up of the leaves and the flower when it has recovered from mowing? However, in the long run, you will have to come to terms with the fact that weeds and lawn do not exclude each other. Only consistent hand-pulling helps effectively! Before mowing! Where does the lawn mix come from? Did you sow the lawn from the same package that is not mixed with weeds? Our wildflower meadow mix looked similar.