Internal links only exist after JavaScript runs

What this means

Most of this page's internal links are absent from the HTML the server sends and only appear once JavaScript executes. Google renders in a second, deferred pass, so link discovery through this page is delayed and unreliable, and crawlers that do not execute JavaScript at all see a near-dead end.

How to fix it

Server-render (or statically pre-render) the navigation and in-content links so they exist as real <a href> elements in the initial HTML response. Client-side routers should still emit crawlable hrefs, not click handlers.

Fix effort

This check needs a developer fix: it turns on a routing, hosting or infrastructure decision that no automatic edit can make safely.

Authoritative source

https://developers.google.com/search/docs/crawling-indexing/javascript/javascript-seo-basics