What is the religious ruling on missing a prayer due to unintentional sleep, and is someone who misses it approximately 10 times considered an apostate?

You must ignore the whispers (waswas) and turn away from them. You should take the means to wake up for prayer. If you miss the prayer due to sleep and do not wake up until after sunrise, then pray when you wake up, and there is no sin upon you, because the sleeping person is excused, and the time for prayer for them is the time they wake up.