Looking for approach to 'flattening' PDFs (suspected jargon conflicts inside)

[Evan0000000000]

First seems like there are two general meanings when people say flatten a pdf:
Converting every page to an image (I'd call this rasterizing if you asked me to pick a term)
or
Removing non visible content and merging content layers down into one

I'm referring to the second thing. Cribbing from adobe (ref: https://helpx.adobe.com/acrobat/kb/printing-complex-pdfs-acrobat.html)

Select Discard User Data.
Select Discard Hidden Layer Content And Flatten Visible Layers, and then click OK.
When prompted, save the Optimized PDF with another new name.

It's possible I'm just not looking in the right places, I suspect .scrub() can remove much of what's considered 'user data' but I'm at a loss for the layer aspect.

My use case is developing a workflow to normalize PDFs from a variety of sources I have no control over so they behave more consistently in the systems I deal with. Following a set of steps in acrobat functionally is fine, but I'd prefer to be able to do this in python so I can fully automate it.

By way of context this is in the print and digital presentation realm, where I've had several vendors assert their products perform best with PDFs prepared in this way, and some even flatly say things like layers (or even vector paths) cause problems.

[JorjMcKie]

Layers in a PDF are used to show / hide certain objects. Depending on the PDF creators effort, this become quite sophisticated.
Often, CAD/CAM exports to PDF embody ways to show or hide construction drawings details, or multi-language documents may support switching between the different languages etc.

Hidden layers are objects whose display is currently switched OFF. This happens via so-called OCGs (Optional Content Groups) - simple normal PDF objects whose meaning in life is to be ON or OFF - nothing else.
Other objects like the mentioned ones and several others (images, annotations, ...) may be assigned an OCG. They will then be shown or hidden when their OCG is switched ON respectively OFF.

Hundreds of OCGs may exist in a PDF, plus complex relationships between their respective ON/OFF states - via specialized other objects which represent logical expressions. You could have things equivalent to IF ... THEN ... ELSE language constructs referring to OCG states, with literally arbitrary complexity.

I am not sue what "discard hidden layer content" may entail: physical deletion of any image, Form XObject, annotation, text, ... that is (currently !) not displayed?
If so, then we must say, that this is not supported in PyMuPDF.

We do however support making arbitrary changes to ON/OFF states (layers) temporarily and also permanently such that the PDF can be saved in each of these respective states.

[Evan0000000000]

Thanks Jorj, I realized as I was writing this question that it must be a pretty complex amount of some kind of work that Adobe is hiding behind "Discard Hidden Layer Content And Flatten Visible Layers"