--New members must uphold democracy, including tolerating diversity.
--New members must be making progress toward a market economy.
--Their military forces must be under firm civilian control.
--They must be good neighbors and respect sovereignty outside their borders.
--They must be working toward compatibility with NATO forces.
NATO's founding members in 1949 included Portugal, at the time ruled by a right-wing dictatorship (1926–1974). Turkey and Greece both joined in 1952, and both have gone through periods of brutal military rule even while remaining NATO members. For the majority of NATO's existence, most of these "requirements" you cite have been mere lip service at best.
Many political scientists classify Erdogan's Turkey as an anocracy – a hybrid form of government which is part-way between dictatorship and democracy, mixing elements of both systems. Yet, Turkey remains a full member in good standing of NATO. Putin's Russia is also often classified as an anocracy. Why demand genuine democracy as a condition to join NATO when its current membership includes a state which isn't one? Indeed, according to the Polity data series [0], Putin's Russia is actually more free than Erdogan's Turkey.
Don't get me wrong, democracy is a truly wonderful thing – but if welcoming non-democratic Russia into NATO might have prevented this war, wouldn't that have been a wonderful thing too?
I wonder, how would the world have turned out if NATO had made a different decision here?
(Just to be perfectly clear, I'm not arguing that NATO decisions justify Russia's invasion of Ukraine.)