Ah, you're right. The issue is the link switching from http to https (even though the supplied link is http) and Chrome making it difficult (by default) to see whether http or https is being used. If I just copy/paste the link it works fine in Chrome and Edge but clicking on the link they both switch it to https. Brilliant.

Just tested, works fine with Safari (mobile, but desktop usually has the same behavior).

The webserver setup seems sloppy. If the site is http only, have https redirect to port 80 or remove the vhost altogether. Not great for an educational institution doing serious computer science.

Chrome's attempt to use a secure connection resulting in 404 while the actual link works fine isn't great. But it's understandable and the TLS-first assumption the're using probably works just fine in the other 99.999% situations.

If only they'd taken the time to copy the http config and setup let's encrypt or cert from GEANT Vereniging CA apparently preferred by rug.nl...

Your browser is sloppy.