In truth I’m no Markdown expert. Indeed my main experience of it is in Discourse forum like this. Having stated my lack of expertise, if commonMark says it supports the pipe-symbol layout you mention above, it _ought to work.
I don’t think we can blame Tinderbox here. it passes the Tinderbox HTML export output to the chosen flavour pf Markdown script. If the script fails to parse it the script has failed.
A teardown test would be to copy the script from the Tinderbox app package and run it from the command line using suitably Markdown-annotated text. If it fails then it is a Markdown issue. If it passes, then there is an internal Tinderbox issue.
i think I’d do the external test first before looking further. I’m wondering if someone familiar with Markdown use and the command line can run such a test.
The Markdown docs aren’t exactly great, so just because it says something is possible it is also possible that some pertinent configuration has been left out. IOW, table mark-up parsing it might need a particular version or later of CommonMark. AS said, one to first test in Markdown w/o Tinderbox involved.
To de-interleave this is unrelated to @webline’s demo which uses action code to make the table, albeit using a pipe symbol as a column date delimiter within lines (paragraphs) of $Text.
Perhaps we should split your issue to a searate thread as it’s actually a discrete Markdown problem?