"Scale to Max" button does not function as would be expected.
The button does currently function identically to how it functioned in 3.6, but that isn't explicitly correct. Models are often scaled to greater than or less than the actual largest size the model could be with the given settings. A large chunk of this likely due to how disallowed areas are handled in cura/BuildVolume.py with the actual functions involved actually being commented by their creators saying that it really isn't an optimal solution and likely doesn't work well on non-Ultimaker machines, which it really doesn't. This needs to be looked into and patched up.
The problem actually still exists upstream, so there is actually a window of opportunity to collaborate with Ultimaker's Cura on a fix for this so they'd be able to have it functional on their branch as well.