As I have the exact same setup, if you are there, we can try a few things.  Let me know.

Let me know what works :) I'm happy to check it out

With regard to your product info screen cap, we have the exact same, with the following exceptions:

1. My BS5/BM5 Application is 7.04.01.1945. Since everything else is pretty much the same, I wonder if you haven't updated to the latest version.  I let mine update itself a couple of months ago and has worked fine since (it also worked fine before).  Others on this forum have confirmed that this version is the latest —and last, in all probability.
2. My BM5 OS Update is 7.03.  Comment is the same above.
3. My BS5 BOM is 5, yours is 3.  I have no idea what this is, but I speculate this characteristic is immutable from the time the device was built.
4. My serial numbers are a bit higher than yours, but that's probably very irrelevant.

  The command on my Mac to connect to the BM is as follows: Finder > Command K > smb://192.x.y.z/BM-SHARE$ Where "192.x.y.z" represents the exact same address as displayed on the BS5 under: Service Mode > Network Info > IP Address From your screen cap it looks like this here paragraph you already have figured out, but it wouldn't hurt to double-check.   My OS is MacOS Monterey 12.6.3 running on a 2014 Dual-Core Intel i5   Other than that, all I can say is that Samba on the Mac sometimes is cantankerous, and that a single-character "A" password might not be welcome by the system.  FYI my BM5 password is more than 20 characters long, and it contains the characters - and $, not necessarily only once, and a mix of lowercase, uppercase and numbers.  I'm not saying you _need_ a long pass, because you obviously do not, but you may want to experiment with at least 9 characters, at your pleasure, but do make the first character a regular letter, just in case.  Remember, the Mac will typically save this password, so you may in fact only have to type it on the Mac once.   One final voodoo thing to try is to reboot both BM5 and Mac _after_ you have entered the new pass on the BM5, and then try and login from the Mac.   Once you get this working, please comment back on this forum, so it may be of help to others in the future.