Apparently I need to be connected to the internet to access the daily shallenge...Obviously my PC is connected as soon as it boots up. Does this happen to anyone else ?

This started happening after "The End is near" update..

I've been trying to find a support system on motiontwin.com in order to submit a ticket but it doesn't seem to exist

I saw your post and tested, and even before "The End is Near" update I can no longer access daily challenge, though I can see the leaderboard. I still cannot access daily challenge after the update. I could access in May 2024, corresponding to my post www.gog.com/forum/dead_cells/how_to_daily_challenge_on_linux_by_running_gog_galaxy_client_via_wine

Judging by that the leaderboard is changing, daily challenge is at least accessible for some people. It is probable that those players are on Steam.

I am not a regular player anymore, but I've seen information about the game being dead and no longer in active development of new content (Notice the gap in deadcells.com/patchnotes on "The End is Near" update, 2023-10-02 is the last time updated before almost a year later Motion Twin / Evil Empire pushed the update from beta branch). That being said, that the update was pushed is still a good sign, and the game might still be supported (e.g. daily challenge issue on GOG). Good luck!

I hadn't thought about that.
Thank you for testing on an older version.

Trying to submit a request through the GOG Support system led me to this : https://support.gog.com/hc/en-us/articles/360008695033-Failed-There-is-a-problem-connecting-to-the-server-while-trying-to-play-Daily-Challenges?input_string=daily+challenge+inaccessible&product=gog

No date on the page however so it could have been submitted 5 years ago for all I know

I have the same problem. The game states that my internet connection has failed, even though the leaderboard updates. This has been happening since the last update.

sebadorn.de/2021/06/28/dead-cells-unlocking-the-daily-challenge-blueprints-in-the-bugged-linux-gog-version mentions how to hack the game to unlock Daily Challenge blueprints on Linux. You may adapt it to your operating system.

Thanks for the tip