Javascript assignment as expression in fat-arrow one-liner
The only thing I think is "bad" when using the one-liner arrow is the implicit return. Whatever the expression evaluates to becomes the return value of the arrow function. In the case of promises, you should be careful when returning from within then callbacks since the return value becomes the resolved value of the promise.

Now in your case, the return value of then isn't going anywhere since the promise is not being used. So it shouldn't matter which form you should use. Therefore it should be fine.

A bigger problem is the entire snippet. You should make sure that project has a value by the time the code using it uses it or ensure that the code using it only runs after you fetch the value of project. If possible, since you have to wait for project anyways, you can make the call to get project synchronous instead.