Upate not shown in Dashboard

My client runs concrete5 v8.5.4 while the website announces v8.5.5 to be the current version (since May’21), but still concrete5 tells that no updates are available… Is this intentional or do I have to assume an error on the website?

With the new community sites and some recent security changes in web browsers, connecting to the community is broken or unreliable.
Your best option will be to download 8.5.5 and update manually.
A prospective 8.5.6 should soon resolve these problems, but you may still need to update to 8.5.6 manually to get the new update code into your site!