I'd like to see this ticket (or another related one) include an exploration of design options, not just name options. I'm not sure you'll ever find a word that's completely unambiguous, but there are lots of other ways to set it off to make it clear it's not a section. Brainstorming some of those:

• Bolding it
• Surrounding it with parentheses or brackets, as done currently on en.WP thanks to @Xaosflux
• Adding or turning it into a carat (^)
• Moving it to the top right corner of the ToC box, across from the word "Contents"
• Making clicking on "Contents" itself be the thing that takes you to the top

The English community appears to be experimenting with this with local edits: https://en.wikipedia.org/w/index.php?title=MediaWiki:Vector-toc-beginning&action=history

My personal solution is to replace it with just 🠕.
I chose to use a non-text replacement, because that is less distracting for me. (If I see text, I read it!).
I tried other unicode arrows, and simply preferred the aesthetics of that one, when shown at the currently specified type size.

As that one looks like OF85 unicode font fail to me, no thanks! An option we were just discussing on-wiki was possibly to include a (horizontal line) under the label; tried to mock that up with styling, but the vector-2022 TOC doesn't render spans.

Personally I like the proposal here to just use the page title. Unlike “Introduction” or “Beginning” it won’t conflict with other section titles. It also probably won’t require special handling from a design perspective, as it’s just another heading and is consistent with all the other links in the TOC

@ovasileva just posted a response on village pump (link to response) which includes this prototype: https://di-toc-first-link.web.app/Moss
moving to Blocked on others until we hear back from people