I also suggest to add option to import index keywords and topic names in a table format (CSV perhaps).

An example of a solution with limited functionality:
Newton; Newton, Isaac (1643–1727)
During import, InDesign would add all appearances of the word Newton to the index, it would appear as “Newton, Isaac (1643–1727)” in the generated index

An example of a solution for languages using declension (semi-smart):
Newton; Newton, Isaac (1643–1727)
Newton\l+; Newton, Isaac (1643–1727)
Based on GREP, InDesign would add not only all appearances of the word Newton to the index, but also all other forms (Newtonovi, Newtonův, Newtona, Newtonem) and they would all appear as “Newton, Isaac (1643–1727)” in the generated index

The generated index should (optionally) automatically shrink page numbers. Instead of:

Newton, Isaac (1643–1727) 26, 112, 113, 114, 115, 170

would be

Newton, Isaac (1643–1727) 26, 112–115, 170

If you manually assign certain Character Style to an index entry (for instance Bold) and the same index expression appears on the particular page more than once, Bold is often ignored when generating the index. It is properly generated only when the highlighted expression is the first one in the list.

I found this index manager last week.
https://index-manager.net/en/indexer-en/?v=3a52f3c22ed6

I generated a list of words from of my indesign file,
exported the word list,
did some fine tuning and imported it back as filter list.

After that i generated my new index in the index manager.

At the moment i am checking out how to get the index file back in indesign.
That is why i found you post here.

I have hundreds of topics i want to add to the index and would take me days to enter them manually.