Thanks to Anthhony, I now have a better option 🙇 Using `<script>toggleTheme('dark')</script>` directly from the markdown given it's already availale from the head declaration. As a bonus, we don't mess with user's preferences for other pages.
Sadly, URLs are more and more hidden into the browser's interface these days… Greatly inspired by Luce Carević! Check out her article too: https://luce.carevic.eu/fr/notes/kirby-mettre-en-place-un-flux-rss