To elaborate on what @MeadowMuffins wrote
check the article
" ImageNet-21K Pretraining for the Masses"
for more details about how to pretrain on this dataset, it's more complicated than regular ImageNet1K, but pretrain quality is much (much) better.
It seems only winter21_whole.tar.gz is available at the official site, instead fall11_whole.tar is no longer possible other than that mentioned by @Lissanro Rayen.
A preprocessing script is given here.
The only place I found where it is possible to actually download full ImageNet: https://academictorrents.com/details/564a77c1e1119da199ff32622a1609431b9f1c47. All other places where I looked either provide just a small portion of it or have broken links, even image-net.org.