doom-emacs uses evil-vimish-fold to control folding. There's no icons in the gutter, so keyboard shortcuts/commands need to be used.
za - toggle fold
zc - close fold
zo - open fold
zm - close all folds
zr - open all folds
https://github.com/hlissner/doom-emacs/blob/develop/modules/editor/fold/README.org https://github.com/alexmurray/evil-vimish-fold