You can sort of do that using these directions to download your Chatmails to Maildir format and view them with Neomutt. Technically, though, that solution bypasses Deltachat entirely: Deltachat and Neomutt are two independent mail clients downloading the same mail from the same server in parallel.
I should perhaps write up a more minimal download-to-Maildir tutorial, though there must be some on the Web.
Maildir export from Deltachat seems fairly unlikely. Thank you for bringing my attention to this archiving work.