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Adobe FrameMaker has been doing real table footnotes attached to the table correctly for about a quarter century now (long before Adobe bought it). There is no question Adobe knows what a real table footnote is, and how to implement it well.
After 20 years of asking for real table footnotes in InDesign with no success it's pretty clear the FrameMaker team holds the InDesign team's leash... at least regarding this one small but important feature.
At least the FrameMaker team is allowing the InDesign team to implement table footnotes horribly. Better than nothing.
Real table footnotes will come to InDesign when FrameMaker dies, but that will likely be long after you do. FrameMaker is a minor but apparently profitable product for Adobe, who just invested in a total 64 bit rewrite of it for the 2019 version.