Thanks to "encouragement" from shibaa987, I've been able to learn a lot and find a solution!
I have an up-to-date install of WP with a child-theme of Realistic, version 1.2.3
I have been an avid user of "Advanced Code Editor" plugin. (https://wordpress.org/plugins/advanced-code-editor/
While looking thru the "codex" for bbPress, I happened to come across some very precise pages on customizing the look/feel of bbPress.
Look at: https://codex.bbpress.org/bbpress-styling-crib/
About mid-way in the part 2 (of 3) there is a specific section that describes how to get bbpress.css to be integrated/managed with a CHILD theme.
Basically it implies that you create a folder named "css" in your child theme's "home" and copy the bbpress.css from the plugin/templates/default to the child theme's css folder.
I was able to SEE even the smallest change made to the child-theme/css/bbpress.css file by refreshing a browser showing the opening page of my forums.
HOWEVER, for some unknown reason, the "Advanced Code Editor" doesn't recognize the "css" folder when I wanted to edit the "clone" of bbpress.css.
So I had to fall back on one of the earliest system administrator "tricks" I learned in the early 1980s as I became a UNIX system admin->guru/consultant.
I logged into my host with "putty", navigated to the realistic-child-theme folder and executed "the trick":
MyHostname $ ln -s css/bbpress.css bbpress.css <ENTER KEY PRESS>
Refresh back in the Advanced Code Editor and "voila"....behold the miracle: I can now see the bbpress.css is available to the code editor to search/edit, etc.
it's called a "symbolic link" and it basically tricks the operating system into showing a file as in a local directory/folder when in fact it actually exists elsewhere.
Hopefully, this will be of some interest to someone. I'd be honored to entertain PMs regarding this idea, but I may or may not be monitoring follow-up posts to this thread if you happen to use that instead of PM.
San Antonio, Texas