You have to add it as a custom action on the sheet, they also say that in the beginning of the post that it is not fully supported

Thank you I didn't see that on the initial read-through.

As near as I can tell, I can't purchase individual elements of Book of Many Things like I could with previous books.  Is that accurate? If so, did any of the PTB say why?

Likely due to greed. Either buy the whole thing or you're not worth renting Hasbro IP in the shareholders' eyes.

And the IT people are forced to work on the VTT under ex-Zynga people, so no one has removed the user-friendly ability to buy individual stuff yet due to overwork.

At least, that's what I suspect.

Issue: Content from the Book of Many Things not being found by the DDB search bar

Context: this is an issue I observe for Planescape (thread here: https://www.dndbeyond.com/forums/d-d-beyond-general/bugs-support/192861-planescape-content-not-appearing-in-search-results) and now I realised is the same for Book of Many Things

How to replicate:
1. go to the DDB search bar and search "seelie market"
2. observe that the only search result is a stat block of a monster

What else appear as a search result to "seelie market"?
This page from the compendium should also appear as a result: https://www.dndbeyond.com/sources/tbomt/jester#SeelieMarket

This is happening to several topics, I observe that the DDB search bar doesn't seem to be capturing the part of the URL that comes after the # for all subchapters in Planescape and the Book of Many Things.

Quote from Sillvva >>

The current official word is this:

Individual items are not available for purchase on Book of Many Things. This will not affect your previous purchases. You will still be able to make a la carte purchases for all products that have always had a la carte purchasing.

We do not have additional information to provide at this time. When we know more, we'll post it here.

 BOOOOOOO!!!!   Bring back availability of individual items!!!   *SHAKES FIST ANGRILY*