After reading your last reply and then again your initial post, it’s clear that you should definitely be splitting documents that large into more smaller ones. So the main paint point for you seems to be the search function. What exactly do you find unusable when it comes to the current search function?
A TOC or an outline as a widget in the sidebar wold also indeed be a lot better than your current approach, especially if you, for instance, split that one document into three or four. You could easily fit the entire TOC in the sidebar then. I’ve mentioned the outline as a widget idea here .
What @qualquertipo has mentioned is probably the best long-term solution for linking blocks. You could easily link blocks if they were object themselves. You can like their linked post if you would love this to be implemented.
Another solution is embedding or transclusion. Usually features like that also allow you to just link to the block or object itself instead of embedding/transcluding it. Here’s a link to one of the feature requests that mentions linking to objects + transclusion.