In a recent amendment to the new model building environment, there is now an 'Edit' button that needs to be selected before a model builder is able to amend an existing formula. This only appears when 'expanding' the formula bar.
Whilst I could perhaps understand the reason for this addition in preventing unintended/erroneous formula edits, the reality is that it is incredibly frustrating for someone used to using a keyboard shortcut (e.g spacebar) or even double clicking to initiate the formula editing process.
I would suggest this new feature is either scrapped, or an optional element of model building UX that could be toggled on / off. This might be something a new Anaplanner would utilise whilst working within a built model.

Anaplan, being a web based application has many areas that require clicks vs. keyboard shortcuts. Adding another one of these in a highly utilised aspect of the tool seems counter productive.