It’s stuck at “Loading…” on both Brave with no extensions and Safari with adblockers. It was only after I tried it on Firefox without anything that I realised the cookie banner is the issue.
In Firefox with ublock origin, I got in the console:
"Loading failed for the <script> with source “https://uncrossy.com/js/cookieManager.js”." looks like a false positive in the ad blocker. Allow-listing the site fixed it.