You said, ‘a bookmarks folder’ . . . not ‘the bookmarks folder’.
If one or more Bookmarks sub-folders suddenly are missing, that is usually because something has corrupted the Bookmarks [JSON] file.
Or, an imported (example filename:) bookmarks_5_20_22.html file has been corrupted. (If you exported your Bookmarks on May 20, 2022, then the resulting HTML file will likely have that filename.)
The ‘corruption’ may be just a single character - missing from a particular place that affects the structure of all, or most of, the bookmarks listed in the file after the occurence of the missing character. (PS. I recently went thru that experience; ‘Where? Are the rest of them?!’ I wondered. I spent hours finding the single character that was missing from where it was needed, in the file.)
I often recommend that users routinely back up their Bookmarks manually, using the Export function in the Bookmarks Manager.
I also recommend routine backups of the BraveSoftware folder:
Linux OS:
/home/$USER/.config/BraveSoftware/
Mac OS:
$HOME/Library/Application\ Support/BraveSoftware/
Windows OS:
%USERPROFILE%\AppData\Local\BraveSoftware\
I would also make a compressed version of the BraveSoftware folder, and be sure that is copied to some external, attached drive. Recommend WinZip or 7-Zip.
In general, I have found GoodSync to be a good backup application.
–
From what I find among Brave Community members’ reports, the odds are, that you are likely to recover / restore Bookmarks IF you have backed up your Bookmarks.
On the other hand, Username - Password (“U-and-P”) combinations are tricky. Because the Passwords are encrypted, and their encryption depends upon a keychain or keyring aboard your Operating System. A new installation or re-installation may upset the important key / digital certificate within the keychain / keyring, that is associated with encrypted items within your BraveSoftware folder.
If you lose the keychain or keyring of that U-and-P association, the odds weigh against your figuring out what those passwords, were. (That is why I recommend a Password Manager such as 1Password, or others, as a Password backup plan.)
–