I'm even more confused now; the 1099-R, if there is one that reflects overcontribution condition and corrective distributions for the employee name on that 1099-R for their 2019 correction, is or is not the Spouse that has no 2020 taxable compensation and wants to have a spousal Trad IRA contribution made on their behalf?

"Is it correct that the FMV of an IRA on the 5498 impacts the taxable amount of a distribution (where there are also contributions)?"

You stated there is no basis, which yes, would typically affect the taxable amount of a distribution. But it's hard to tell if there is excess in an account; excess in an account means it affects the FMV the same as having Basis.

You have too many details in the scenarios where you are asking vague questions of people on the internet. What you need to do to understand how these things all impact each other, across years, account types, etc, is to take them in order and by account/plan type. For instance, a 1099-R with P means that should be reported in 2019, and if you are working on 2020, that distribution would be moot.