This once I am going to answer something like this here, on the main group, since it's short. That being said, this is not an NVDA question, it's a Chrome question. What you do in bookmarks manager to achieve what you want to achieve is the same regardless of the screen reader involved. Questions about how to use specific pieces of software belong in the Chat Subgroup with the exception about inquiring about whether a given piece of software is accessible with NVDA or not.
1. Open the Bookmarks Manager, CTRL + Shift + O
2. Gain focus on the tree view for your bookmarks. Mine happens to have Bookmarks Bar as the very first item, but depending on what you've done, and when, yours may not.
3. Hit CTRL + A to select all. If you wish to, jump over to the bookmarks items and double check what's selected.
4. Navigate to the Delete button, which only becomes visible/accessible after items are selected, along with a Cancel button, and activate it.
All your bookmarks should be deleted, provided all were actually selected. If you happened to miss a folder or two, repeating the process is still much, much faster than one-by-one deleting is.
Brian - Windows 10, 64-Bit, Version 21H1, Build 19043
Nothing in all the world is more dangerous than sincere ignorance and conscientious stupidity.
~Martin Luther King, Jr.