For what it’s worth, you can use markdown to include links without formatting.
but anyway, it looks like it’s just that the old Pixar redirect to OpenUSD has stopped working, but technically the usd docs haven’t lived under Pixar’s domain for many years now.
Apologies, we’ve been re-working how graphics.pixar.com is hosted, and this probably impacted the redirects as Dhruv noted. OpenUSD docs were moved to openusd.org a while ago as well.