"So it would appear to me, per IRS Notice 2020-65 reading, employers ARE required to defer withholding (and payment thereof) of employee portion of OASDI if wages paid between September 1 - December 31, 2020, are under the applicable wage limit. Employers/employees have no choice. Is that everyone is reading?"

Nope.

It states only that the Employer is considered the affected taxpayer, and the deferral has to be computed on specific wage limits and repaid by a specific timeframe, and how it can be collected is specifically not stated.

Employers apparently have the choice to participate or not.

And it doesn't address the Employer share; yet, they are identified as the affected taxpayer.

It's still a big mess.

Employees get to do what that employer had decided to do, based on what qualifies.