einvoice-preflight now has a page for Finland, both linked from the all-countries table. Neither country has a domestic business-to-business mandate that any source found puts a date on. Austria has required electronic invoices from suppliers to federal bodies since 1 January 2014 (ebInterface or Peppol BIS 3.0). Finland takes Peppol invoices in government and reportedly lets a buyer ask for a structured one. The first fixed date for cross-border B2B in both is 1 July 2030.
The Finland page is built from search excerpts of vendor and advisory guides. The ministries and the laws could not be read, so each page says so, states no penalty, and lists where sources disagree (Austrian regional reach; a 2027 to 2028 Austrian date one firm expects). The checker applies EN 16931 and Peppol rules; it has no ebInterface or Finvoice reader yet, and says that on the page. A summary, not tax advice.