Warning: You should probably just do what @Mattches says and use the export/import feature unless you like extra work and risk.
If you just want the bookmarks, then yeah, the export/import should work. My memory [edit: fuzzy because of time and events since] is that the way they were organized may not have carried through, but I did an export/import months ago and that may have been fixed. [edit: probably has been fixed if was even a thing]
Most extensions you install live in your profile folder’s Extensions folder, so they and their preferences should follow with the copy. I had extensions and other things I wanted to carry over, plus the way my bookmarks were organized, so I opted to try the copy. I admit it introduces some risk to stability, but it was worth it to me, and I don’t recall having any significant problems.
The profile folders are in ~/Library/Application Support/BraveSoftware/Brave-Browser-Dev/ (or the Brave-Browser folder corresponding to your currently used version: Brave-Browser, -Beta, -Nightly). Each Brave version (release, Dev, Beta, Nightly) has a separate folder in the BraveSoftware folder.
The profile folder you use is probably just called Default and that may be the only one if you haven’t added profiles.
If there’s more than one, the others are usually titled things like Profile1, Profile5, etc. The one with the most recent modification date is usually the one you want. Because I used Release instead of Nightly in the pics above, the modification time is from when I did some testing in Release instead of my current use of Nightly to post this.
That’s pretty much it.