What Durham says in his report is:
That the FBI probe was “seriously flawed” with no grounding evidence and that FBI officials “discounted or willfully ignored material information that did not support the narrative of a collusive relationship between Trump and Russia.”
And that:
“(Hillary) Clinton allegedly approved a proposal from one of her foreign policy advisors to tie Trump to Russia as a means of distracting the public from her use of a private email server,”.
In other words it was a hoax, likely instigated by Clinton and the DNC, which had far-reaching detrimental effects for Trump, and was, having begun in mid 2016, an attempt at election interference.