problem with tex4ht 20200327

[Karl Berry]

    The test1x.gif was not generated.

Hi - it seems this has been fixed since the original TL20 release. When
I run your test file (thanks for providing it) with the current TL, I
get the test1x.gif output again.

Michal Hoftich has been actively maintaining tex4ht, so if you're using
tex4ht, it is good to use current TL. In theory you can update with
  tlmgr update tex4ht
although I fear in practice it's probably necessary to update everything
with tlmgr update --self --all, since many changes to tex4ht have been
required this year due to changes in LaTeX.

You can also submit tex4ht bugs either on the tex4ht at tug.org
(https://lists.tug.org/tex4ht) mailing list, or the bug tracker at
https://puszcza.gnu.org.ua/bugs/?group=tex4ht.
Michal will see it either way.

We've also been updating the doc and web pages at https://tug.org/tex4ht.

Hope this helps,
Karl