And how do we know that the spotlight index is being rebuild? And how do we know how much time it is going to take? And how do we know when it has finished?

I find the procedure to ask for the spotlight index to be rebuild cumbersome and weird. Adding a folder for exclusion from search and then deleting it is the most weird thing ever.

You could use the straightforward and clear-cut procedure in the terminal.

sudo mdutil -E <path/to/reindex>

To reindex the entire startup volume

sudo mdutil -E /

Or, just Documents

sudo mdutil -E ~/Documents

If you click the menu extras Spotlight icon 🔍 and a blue progress bar appears, then you know Spotlight is still indexing your drive.

I almost never rebuild my Spotlight index and that has not adversely impacted by daily Mac usage. Personally, I don't want an additional GUI item popping up misinforming me that Spotlight will be done indexing in __ seconds or minutes, as it is irrelevant to my other parallel activity during that indexing process.

Feel free to share your thought with Apple.

Feedback - macOS - Apple

+1

There will also be a progress bar when doing a Spotlight Search if it is indexing. Also not particular useful.