Hello and welcome @Lukas!
You may look at the whole thread here for history on this question: When will PDF/A export be available? - #19 by quachpas.
The feature request is tracked here: Add PDF/A-1b native export · Issue #5189 · typst/typst · GitHub
You might want to try one of the many pdf conversion tools listed (try https://facile.cines.fr/) for PDF/A-1b compliance. If doing it online is not possible, then try using ghostscript. I think the conversion commands are listed in the previously mentionned thread.