Title tag changes when JavaScript runs

What this means

The <title> in the server's HTML is not the <title> that exists after JavaScript executes. Google may index either version depending on when rendering completes, so the title shown in search results becomes non-deterministic — and the raw-HTML title is the one used until the render queue catches up.

How to fix it

Emit the final title in the server response. If a framework sets the title client-side, move that into server-side rendering or the static build so the first byte already carries the correct title.

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