NATO membership is popular among Ukrainian people, largely because of Russia’s actions over the last 20 years during which time support has risen from roughly 20 to 60 per cent.
The criteria are pretty vague:
This from NATO’s website
“European countries that wish to join NATO are initially invited to begin an Intensified Dialogue with the Alliance about their aspirations and related reforms. Aspirants may then be invited to join the Membership Action Plan, a programme which helps nations prepare for possible future membership. Participation does not guarantee membership, but is a key preparation mechanism.
To join the Alliance, nations are expected to respect the values of the North Atlantic Treaty, and to meet certain political, economic and military criteria, set out in the Alliance’s 1995 Study on Enlargement. These criteria include a functioning democratic political system based on a market economy; fair treatment of minority populations; a commitment to resolve conflicts peacefully; an ability and willingness to make a military contribution to NATO operations; and a commitment to democratic civil-military relations and institutions”
There was no real talk of Ukraine joining NATO until Russia Starmer threatening it, which also explains why other countries which previously been happy to stay out then started to think again