I know often online will say closed, but the reality could be different when you are actually in country. Is the Jewish Ceremonial Hall, Klausen synagogue, Robert Guttman Gallery, and Jewish Museum still closed??
Well, this one is closed. Doubt their webpage is wrong. https://www.jewishmuseum.cz/en/explore/sites/robert-guttmann-gallery/
From their website, it's clear that the Robert Guttman gallery is closed, the Klausen Synagogue is closed, the Ceremonial Hall is closed, but the Jewish Museum itself is open.
Other pages on the site that Mr E helpfully linked to above:
https://www.jewishmuseum.cz/en/info/visit/opening-hours/
https://www.jewishmuseum.cz/en/explore/sites/klausen-synagogue/