I have not been able to generate opam files from dune files in 2.0. Here is a minimal example that works to generate an opam file with dune 1.11.4 but does not lead to a generated opam file for dune 2.0:

(lang dune 1.11)
(name foo)
(homepage https://my.home.page)

(generate_opam_files true)

(package
 (name foo)
 )

I'm guessing we also need tests to guard against this regression in the future.