Even if it isn't able to do it based on a page range, how about a Section range? The work arounds are so needlessly time consuming, including having separate files for the chapters and then creating a New Book or the other: "To display only a range or a section, we need to first add a Paragraph Style to the TOC. In my case, the Sections headline will work to limit my range, but if you don’t have anything like that in your layout, you can place some hidden text right above the first “headline” and right after the last one. You could put the text on a hidden layer, but personally, I prefer to change the formatting of the text to make it invisible because then I can put it in a threaded text frame with the range of headings that I do want to appear in the TOC." You have smart people at Adobe. I'm sure one of them could program a simpler way to do multiple
Tables of Contents in one long document.

You can do this if you use book files - you can generate TOCs from just the current document or the entire book

I agree with this completely. Most of the long documents I make require multiple TOCs and having to designate different Paragraph styles to pull for the range I want isn't very practical.

This would be so great!

(Also, Stefano Bernardi's suggestion, while appreciated, is not in any way simple nor a reasonable replacement to the missing in-app ability.)

I like this idea!

You can already achieve this in a pretty simple way: https://indesignsecrets.com/table-of-contents-subsection-long-document.php