A copy of a message I just sent to the tldistro list, for the record here. .. for TeX Live 2019, the t4ht program will expand %%~ to $TEXMFDIST (set in texmf.cnf) instead of $SELFAUTOPARENT. This means the tex4ht.env file should use stuff like i%%~/tex4ht/ht-fonts/iso8859/1/! instead of i%%~/texmf-dist/tex4ht/ht-fonts/iso8859/1/!
Perhaps distro versions have already been doing this, since the SELFAUTOPARENT expansion was probably not useful, but I thought it was worth mentioning. References: https://tug.org/pipermail/tex4ht/2018q2/001975.html (thread) https://puszcza.gnu.org.ua/bugs/index.php?394 TL19, including this change, is currently being pretested -- https://tug.org/texlive/pretest.html. If anyone has patches to be included, please let me know asap. Thanks, Karl