To a large degree, the same internet that used to be, still is.

Keep in mind that in the era they are nostalgic for, the internet involved roughly 4% of the world's population. As big in the public conciousness was, it was a relatively small thing.

For example, most people see Lemmy as pretty small and much slower content coming at you than reddit. However Lemmy is still way bigger than what a mid 90s experience with the internet would be. I can still connect to play BBS Door games and there's barely anyone there, but there were barely any people there back then either. The "old" internet is still there, it's just small compared to the vast majority of the internet that came about later.

Some things are gone, but replaced. For example Geocities now has neocities, which is niche by today's standards, but wouldn't be shocked if neocities technically is bigger than geocities ever was in absolute terms.

Some things are gone and won't come back. The late 2000s saw a really nice and stable all-you-can-watch streaming experience from Netflix, and their success brought about maddening licensing deals where material randomly appears, moves, and disappears and where a lot of material demands more to "rent" than buying an actual Blu Ray disc of it would cost (have gone back to buying discs as of late because it's cheaper than streaming).