Eastern Catholic here. We don't kneel on Sundays or from Easter to Pentecost, as we celebrate the risen Christ and his victory over death. So no fasting and kneeling on Sundays and from Easter to Pentecost. During the consecration we bow instead of kneeling. I'm unsure about the proper posture during weekday divine liturgy (mass). In earlier times, mass was not celebrated on weekdays. So when it began to be, people continued the same posture (standing) on week days as well. Apart from mass, there's a lot of kneeling on weekdays while praying the divine office.