SOLUTION:
To their credit, the Sony has maintained FCP support for it's log and capture software (Catalyst Browse aka CTB) across the more than a decade of life the XDCAM technology has seen. Turns out there was a 0.0.1 update to the software that fixes the issue. I've been using XDCAM so long I forgot that package installs the software used by FCP to handle the XDCAM file structure. So if I had said YES to the prompt to update CTB to version 2026.1.1 from 2026.1.0, this would have been avoided.
In my defense I have been burned in the past by updates to that package ... hence the reluctance. But being a laggard burned me this time. #cantwin
EPILOG:
At this point Sony has migrated to the Free or Subscribe model and renamed Catalyst Browse. So for any XDCAM users who find this thread, you must upgrade to the V3 package of the Sony Catalyst Prepare software (here). It's safe to go in the water ... It works on Tahoe 26.7 and FCP 12.3
p.s. Drag/drop of the BPAV folder still does not successfully import XDCAM files. You must use the IMPORT dialog.