This scripts allows the export of PostFinance account flow data for YNAB 4 using Tampermonkey. The export is not based on the CSV generated by the Post as it does not adhere to the standard but makes use of the data loaded on the client side for doing said CSV export.
If Tampermonkey is installed you can click on the RAW view of the postfinance-ynab.user.js
file of this Gist.
Tampermonkey should ask you whether or not you would like to install this script.