Thank you, Jakob, for your answer,

I didn't think that my example was too complex.
pdf/A-2a works with ConTeXt, it is recognized as pdf/A by FoxitReader. However, I would like the result to be valid, as with pdf/A-2u.

Does anyone else have any tips or ideas? Is it not that important?

Greetings
Thomas

Am 12.09.24 um 15:52 schrieb Jacob Kauffmann via ntg-context:

I don’t know about the ConTeXt way, but I have done it in the past with Adobe Acrobat Preflight and pdfaPilot (https://www.callassoftware.com/en/products/pdfapilot), both granted through my institution.

In complex documents, there are often things that ConTeXt cannot solve for you, such as missing color palettes in external figures etc.