I found that there are other hyphenation rules in my language package (https://ctan.org/tex-archive/language/hyphenation/ukrhyph). How can I activate not default hyphen rules? By default Ukrainian language settings use very liberal hyphenation rules.
MWE https://www.overleaf.com/read/nrqycybcgprp
\documentclass{article}
\usepackage{polyglossia}
\setmainlanguage{ukrainian}
\setmainfont{Noto Serif}
\begin{document}
\parbox{0em}{хімічний}
\end{document}
Produces хі-мі-чний, but with ukrhypmt.tex should produce хі-міч-ний
pdflatex
and T2A encoding.\showhyphens{хімічний}
is a better way to see hyphen points in general, the 0 width parbox would not work in xetex for example as xetex like pdftex does not hyphenate the first word. You can use\hyphenation{хі-міч-ний}
to specify that rule.