I'll be dating myself a bit here but I got some good ones (at least I think so).
Youtube used to be something of a social media type website, not dissimilar to myspace or facebook in many ways. You could leave comments on people's profiles, the profiles had an element of customization and there was a sort of group function that allowed you to join communities where you could post topics and have discussions about whatever. When youtube decided they were gonna drop that group function a lot of people were super upset and I remember there being some talk about the site actually dying because of it. Obviously this sounds silly today but at the time, well you had to be there I guess :P
Another huge thing was when megaupload/megavideo was taken down. Those websites were the backbone of so many fandoms and online spaces. Entire blog websites died because now all their links (to music, videos, photos, anything!) were dead and there was no way to retrieve the content. Websites dedicated to anime/cartoons were just fucking gone because everything on there was hosted via megaupload. This was before all the streaming services we have now and streaming as a concept on the internet was hit pretty hard. Of course other things would replace megaupload eventually and there had been several other sites doing similar or the same thing (hosting content) but megaupload had been by far the biggest fish around so for a while the internet really was in shambles it seemed. You can still find relics of this time if you look for it, particularly some old blogs for example, with dead links to some content that no longer exists. If you like going on deepdives and exploring the internet's past it might be worth a look.