Had the same issue, and appear that I cannot be used with output: "static" and for now Astro@5 we can only use output: "server" and this fixed the issue but ofc we need to handle different deployment by that.

used this solution

---
const initialTag = Astro.url.searchParams.get("tag") || "";
---

tried to fix it to work with output: "static" and marking the page as not prerendered:

---
...
export const prerender = false;
---

but after build it appear - it doesn't work