This has been a HUGE problem. I teach a magazine design module where I implore students to plan because the layout adjustment function is so powerful, only to find it no longer works. I've been demonstrating this from when it first appeared and it can shave hours off a project.
Also it gives a warning triangle when you select a different number of columns in the options?!?! One of the most useful parts, but allows margin size changes? It's not often that you'd change these in a magazine where you need consistency.
PLEASE fix this.

Adjust Layout is new to CC 2019. I haven't personally found any reason to use it yet. It seems to be for cases when you need to change the size of a document. From my point of view, this would require changing/adjusting so many details that I would not feel comfortable automating it. I would want to adjust everything manually, to make sure every detail was addressed, adjusted, and locked down how I wanted.

Layout Adjustment is a feature that was REMOVED in CC19 that will adjust the contents of your page (according to a few straightforward parameters) if you change the margins (or, I suppose, the document size). When working with large multi-page documents with multiple master pages (regular text page, short/long text page, chapter openers, part openers, etc), Layout adjustment made it quick and simple to start a new chapter by applying a chapter opener master page. The text boxes on the page would simply and automatically resize to fix the new margins. No need to manually close or open up text boxes every time. It also made things super simple when you're still in the design stage, trying to work out the ideal margins. If you decide to need to make the outside margin a few points wider, you just had to adjust the master page, and text would all follow suit. On a 400 page book, this is indispensable.

For book design, I'd consider Layout Adjustment one of the top essential tools in InDesign. Please bring it back.

I am using Adobe InDesign 2019 and cannot find "Layout Adjustments options" in no menu on my Mac. I am attaching a screenshot of my Layout menu. Why is this happening?

What do you mean? Adjust Layout is a new Feature of CC 2019 ?!