When using the functionality SPC h f to describe a function, then for example face-spec-set, this will open a pop-up buffer in helpful mode. Then navigating to one of the links in the document, e.g. defface, with RETURN opens a new helpful-mode document describing defface. There is no way to go back to the first page.
There is an issue and a pull request related to adding this functionality in helpful, but the repository is nearly inactive.
Doom is using advice-add to override the default help-mode to use helpful-mode. The help-mode does have the ability to navigate back using C-c C-b, but helpful-mode does not. This makes navigating the documentation very hard.