Adobe PDF Export presets (.joboptions) that work in ID, PS do not appear as options in Save As > PDF in AI.

Edit > Adobe PDF Presets... show they are installed. Attempting to Install them manually returns an error: "The preset '[XX.joboptions]' is not recognized as a valid .joboptions file." They cannot be Edited nor Exported from this dialog. (Even though they can be Edited and reimported in other apps.)

Affected presets use PDF/X-4:2010 Standard.

Illustrator requires PDF Export presets specifying Standard PDF/X-4:2007 or lower/None.

Creating new presets within Illustrator and selecting "Standard: PDF/X-4:2010" in the dialog actually creates .joboptions files specifying compliance with PDF/X-4:2007.

This can be verified by opening the .joboptions files in a text editor. (I used BBEdit.)

Simply opening a non-working preset (works in ID & PS, but not available in AI) as text and changing the line:

/CheckCompliance [
/PDFX4:2010

... to PDFX4:2007 renders the preset functional again.

This has been tested on Illustrator versions CC 2017, 2019, and 2020 on multiple machines; Mac OS Sierra, High Sierra, Mojave.

this follows from this Adobe Support forum thread:
https://community.adobe.com/t5/illustrator/my-adobe-pdf-presets-don-t-show-up-in-illustrator-cc/m-p/10861208#M162030

Steps to recreate:

Create a PDF preset within ID (any version after CC 2015) that specifies Standard: PDF/X-4:2010.

Verify this same preset is valid and functional in ID & PS.

Open any file in AI (versions 2015-2020). File > Save As with option Format: Adobe PDF. In the Save as Adobe PDF options dialog, under "Adobe PDF Presets:" the custom .joboptions file is not present in the list.

Under Edit > Adobe PDF Presets... in the list of installed presets, the custom .joboptions file is listed. Selecting it, both Export and Edit are grayed out.

Selecting "Import" and selecting the same .joboptions file returns an error: "...not a valid .joboptions file."

Create a New PDF preset within Illustrator. Specify "Standard: PDF/X-4:2010." (2010 is the only X-4 option.)

Verify Edit and Export options are not grayed out and function.

Verify preset works in ID & PS.

Open both presets (Mac OS: /Users/[username]/Library/Application Support/Adobe/Adobe PDF/Settings/) with a text editor.

Find the lines beginning with: "/CheckCompliance" and the immediate line after:

Files created in ID will read:

/CheckCompliance [
/PDFX4:2010

Files created in AI will read:

/CheckCompliance [
/PDFX4:2007

In AI (Edit > Adobe PDF Presets) and ID (File > Adobe PDF Presets > Define...) both report "Standards Compliance: PDF/X-4 2010"

In text editor, for preset created in ID, manually change:

/CheckCompliance [
/PDFX4:2010

to "/PDFX4:2007" — Save preset.

Verify PDF preset that was previously unavailable in AI, File > Save As, Format: Adobe PDF is now present and functional.

Under Edit > Adobe PDF Presets... preset now has Export and Edit buttons enabled. (Preset still reports "Standards Compliance: PDF/X-4 2010")

Resolution: Either create all PDF/X-4 standards-compliant PDF export presets within Illustrator for the rest of the CC suite; or manually edit all .joboptions files created for PDF/X-4 standards-compliance from "2010" to "2007."

This may present an issue where strict adherence to the 2010 version of the standard is critical and required. Although PDF's are exported with "2010" selected, they are actually only compliant with 2007, the only version AI understands.