Avogadro 1 is not under active development, the repository was archived in September 2021. Development of Avogadro 2 is being done at https://github.com/openchemistry/avogadrolibs. Avogadro is an advanced molecular editor designed for cross-platform use in computational chemistry, molecular modeling, bioinformatics, materials science, and related areas.
When I open an xyz file that Avogadro detects as open shell, the popup window does not disappear when I click 'no', only after I click 'yes'.