I had a 5090 some months ago but couldnt get flash attention to work. Does it now work natively? What about 5080?

Pytorch now has native support for the Blackwell architecture:

https://pytorch.org/blog/pytorch-2-7/

Curious what issues you were having. The kernel should compile natively if you pass nvcc the correct arch flags, although it probably won't take advantage of any new hardware features.