@GAERTNER Lukas Thanks for your patience! PG team identified the bug and manual workaround to this bug is after the creation of the workflow in designer view, you can go to code view and update the schema replacing the "~2" with "[" manually and save it.
here is the private azure portal url with the fix https://ms.portal.azure.com/?Microsoft_Azure_EMA=carlos
The fix is not fully deployed to prod, ETA for it will be mid-December or mid-January
please try and do let me know incase of further queries, I would be happy to assist you.
If you found the answer to your question helpful, please take a moment to mark it as Yes for others to benefit from your experience. Or simply add a comment tagging me and would be happy to answer your questions.