BBPress doesn’t provide these buttons for posts by default?
When starting a new topic, type some text in the content box, note the right click menu doesn’t show Undo. It will in the topic title box, and when selected, undoes the text in the original content box.
When more text is added, the Undo appears on right-click, but no Redo Unfortunately, and in Edge, Ctrl-Y isn’t mapped to anything.
There may be a plugin for it somewhere, related: @mention autosuggest in visual editor.