Resolved - Time Machine Backups to external HD fail(ed) after Big Sur

First, I give full credit for information gleaned from article entitled

“macOS Big Sur supports Time Machine on APFS-formatted drives, but there are a few catches”

By Glenn Fleishman, Senior Contributor, DEC 14, 2020 9:00 PM PST

and I apologize for possible misinterpretation thereof.

https://www.macworld.com/article/234913/macos-big-sur-supports-time-machine-on-apfs-formatted-drives-but-there-are-a-few-catches.html

> My Pre Big Sur Environment:

Macbook Air mid 2013 running macOS Sierra (10.12) using HFS+ file system with internal SSD drive.

Backups using Time Machine were successfully running to external HD (LaCie) USB External Physical Volume • Mac OS Extended / Case-Sensitive Journaled HFS+

> Post Big Sur:

This release upgraded my SSD based Mac from HFS+ to APFS.

(FYI - I think this would have happened anytime with High Sierra 10.13 or later, but I didn’t upgrade from 10.12 until Big Sur)

Big Sur also provided for Time Machine backups to APFS formatted drives. 

> The problem, as I interpret, was that this version of Time Machine was now looking for a drive with a single “container” native to APFS format.

Since my LaCie is still formatted HFS, I can’t continue to use it as a backup destination unless I reformat it.  

Since I also didn’t want to lose all information currently stored on that drive, and didn’t have another, I purchased an SSD external drive, formatted it APFS, assigned it as the Backup destination drive in Time Machine and successfully backed up my Mac!

BTW, I can still access my LaCie, I just can’t use it for backup.

Thanks again to Glenn Fleishman for valuable info leading to resolution of my failed backups.