Hyperref change breaks every document that I'm writing!

[Karl Berry]

    Installing TeX Live 2019 from: http://ctan.cs.uu.nl/systems/texlive/tlnet

That mirror does appear to be up to date.
http://ctan.cs.uu.nl/systems/texlive/tlnet/archive/?C=M;O=A
(scroll to the bottom) shows that latex.tar.xz and all related dated
October 5, as they should be. What does 
  tlmgr info latex
report? It should be "revision: 52286".

Assuming that's current, maybe you have an old .fmt file shadowing the
one that (hopefully) got rebuilt. Try:
  kpsewhich --all -engine=/ pdflatex.fmt

And then ls -l on the results. Normally there should only be one, and it
should have the same October 5 (plus/minus depending on time zones) date.

Hope this helps,
Karl