What are the major deviations from the Buddha’s original teachings in later Buddhist traditions, and how can a lay follower avoid them?

Buddhism has developed into many schools and traditions since the time of the Buddha, each with its own interpretations, practices, and philosophical systems. While this diversity is valuable in some respects, it also raises the concern that certain ideas or practices may have strayed from what the Buddha himself originally taught. This raises the question of what counts as a significant deviation from the original doctrines of Dhamma and how such differences can be identified. I would also like to know how a lay follower can recognize these divergences in a clear and practical way, and how one might remain faithful to the spirit of the Buddha’s message without falling into sectarian arguments.