Hi Lashley,
It seems the puzzles are moving behind a paywall. Some solvers have reported that they can still enter online if they re-register on the observer site.
Alternatively the pdf is still available here, which details how to enter by post and the deadlines…
https://cdn.slowdownwiseup.co.uk/media/documents/obs.GEMELO.20251130.pdf
The same applies for Everyman, unfortunately.