Here’s how Apple translates the St Martin/St Barth portion of the Prefecture’s post:
For travelers between Saint-Martin and Saint-Barthélemy, the same terms apply, whether by air or by sea.
Maintenance of compelling reasons for unvaccinated people from Sint Maarten to Saint Bartholomew
Travellers from Sint Maarten to Saint-Barthélemy by sea must:
• present their complete vaccination status
• and if they are not vaccinated:
• provide a compelling reason (professional, family or health)
• and carry out a 7-day isolation period upon arrival in the territory and a test at the end.
For travelers from Sint Maarten to Saint-Barthélemy by air, the provisions remain unchanged.