I've come to the conclusion that TurboTax Premiere 2022 is defective, as it is incapable of allowing two separate 1095a forms to be entered. As a test, I created a test tax form in last year's Turbotax Premier 2021, and it DOES ALLOW multiple 1095-A forms to be entered. So this is clearly a defect in the 2022 version. I've also tested the current FreeTaxUsa, and it does allow multiple 1095A forms to be entered, and their associated percentage allocations. FreeTaxUsa generates an accurate 8962 form as required for filing (whereas TurboTax's 8962 is inaccurate). If Turbotax cannot fix this defect soon, I'll be using FreeTaxUsa to file, and I'll be saying goodbye to TurboTax.
RESOLVED.
The solution was delete everything from the first 1095-A info I had already entered under the ACA section, and then start the ACA section over from scratch. Only then was I allowed to add a second 1095-A form. Somewhere along the line it looks like I triggered a bug in the software. One has to wonder what other bugginess exists in this software, and whether it affects calculations... I did detailed screen captures showing the problem and resolution, so I can refer to that as a warning in later years.