This form has an “HTML field”, which is just a <textarea> but “improved”
with the use of Automattic’s isolated block editor[0], a repackaged
Gutenberg’s editor playground as full-featured multi-instance editor
that does not require WordPress.
I do not want to use Node to build this huge, over-engineered piece of …
software. Therefore, i downloaded the released “browser” package, and
added the required React bundle, like i do with HTMx. This will hold
until i need a new custom block type; let’s hope i will not need it.
[0]: https://github.com/Automattic/isolated-block-editor