[sbrscnds]

Do all Buddhists believe in the concept of reincarnation?

Many and the most part of Buddhists believe reincarnation and rebirth. Most traditions teach rebirth. Some Tibetan traditions teach reincarnation. For example, Zen traditions that came from the Cha'an Chinese philosophy, all them have a heavy emphasis in rebirth aspects like the notion of humans coming from being insects in previous life. And the like.

Of the very few traditions that offer teachings with no reincarnation or rebirth dressings are, in my experience, the Thai Forest and very few Soto "reformed" schools that, at least, do not make much emphasis in that view, as far as I know.

As a personal opinion, God, rebirth, reincarnation, or "something" that goes from here to there enduring endlessly, is nothing but only existential angst, fear, apprehension, attachment, craving for more, and the urgency of "becoming" or "being". When mind is at peace, still, awakened and clear none of such feelings abide.