I’m a connoisseur of churches, at least pre pandemic. I’ve not been to anything called an “atheist church”, exactly, but the nearest thing is probably the “Sunday Assemblies” that have spring up in various places.
There are more than a few atheists in Unitarian churches (particularly New Unity, in London) probably a few at Quaker meeting houses, and a few spiritual atheist types in very liberal churches such as the Episcopal church (Richard Holloway being an example).
Many Unitarians would describe themselves as agnostic or deist or some other non traditional theist position falling a bit short of outright atheism.