The Biden website was essentially just archived and the new administration is working on building up the site. This isn’t something specific, almost all the old website links are broken.
“It’s day two. We are in the process of developing, editing and tweaking the White House website. As part of this ongoing work, some of the archived content on the website went dormant. We are committed to reloading that content in a short timeline,” -Harrison Fields
The Biden website was essentially just archived and the new administration is working on building up the site. This isn’t something specific, almost all the old website links are broken.
Everything is archived here: https://bidenwhitehouse.archives.gov/