Kindle Previewer not opening automatically from InDesign

That "feature" AFAIK depends on the operating system. Have you tried switching to something else to see if it works there? I'd suggest Thorium Reader.

The "automatically open previewer" function has never worked for me, no matter how I configure either ID or KP. I am not sure where the problem lies. This is true even when I add KP to the "also open" list below. (But then, I can't make ID automatically open Thorium Reader, either, by adding it to the list.)

I simply click on the exported EPUB and that opens Previewer to convert and display it. (Note that KP will open a new instance every time; you may want to get in the habit of right-click/Close All Windows occasionally.)

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Not an expert on Kindle, but I believe it imports the ePub, not opens it. Kindle's default formats are MOBI and AZW, not ePUB.