Just a quick heads up: It will probably take us a while before we can actually use #Bundler 4.0 itself in #depfu.
Today we've fixed an issue with the slightly changed white space in lock files and so far we've seen no issues beyond that in terms of Depfu upgrading dependencies in projects that use Bundler 4.0 but we fully expect issues to appear. So if you see any, please report them to us!
For some reason we expect Bundler 4.0 to ship with #Ruby4, so...