Cannot convert Greek lowercase to uppercase without accents in LuaLaTeX. How can I?

Please consider the following LuaLaTeX compilable code. It supposes to convert a sentence written in lowercase Greek to UPPERCASE, but with no accents. It converts to uppercase but the accents are still there in capital letters. Furthermore, it uses two different ways, both failing. Any suggestions appreciated.

% !TeX program = lualatex\documentclass{article}\usepackage[a4paper, total={180mm,257mm},left=15mm,top=20mm]{geometry}\usepackage[no-math]{fontspec}\defaultfontfeatures{Scale=MatchLowercase, Script=Greek}\setmainfont{STIX Two Text}\usepackage{polyglossia}\setdefaultlanguage{greek}\setotherlanguage{english}\begin{document}ΜικρόΚείμενογιατονέλεγχοτηςμετατροπήςτωνπεζώνσεκεφαλαία    \MakeUppercase{ΜικρόΚείμενογιατονέλεγχοτηςμετατροπήςτωνπεζώνσεκεφαλαία}    \let\acctonos\relax\MakeUppercase{ΜικρόΚείμενογιατονέλεγχοτηςμετατροπήςτωνπεζώνσεκεφαλαία}\end{document}