non-Chinese/Indians/Arabs?

There were many, including one of the most influential: ibn Sina (AKA Avicenna), who was Persian. Also prominent was al-Biruni. There was a strong intellectual tradition in Persia and Central Asia before the Islamic conquest, and this tradition continued - many of the famous Medieval thinkers in the Islamic world were Persians/Central Asians. Al-Ghazali, author of the very influential Incoherence of the Philosophers can also be mentioned as an influential Persian thinker. There were many others.

Al-Farabi, the "Second Teacher" (Aristotle being the First Teacher) was possibly Turkic. If so, he would be the most influential Medieval Turkic philosopher. However, his ethnicity is uncertain, and he might have been Persian or Sogdian.

Another highly influential thinker of uncertain ethnicity was Bodhidharma, who might have been Central Asian (but also might have been Indian).

non-Muslim, non-Buddhist, non-Confucianist philosophers.

The first part of the question was about ethnicity, and this part is about religion and/or philosophical school. Firstly, there are intellectual traditions outside Islam, Buddhism, and Confucianism. In India, there are Hindu and Jain traditions of thought. Across the Islamic world, there were many influential Jewish and Christian thinkers, and in China, there were non-Confucian traditions such as Daoism and Mohism (with Zhuangzi AKA Chuang Tzu AKA Zhuang Zhou and Mozi AKA Mo Tzu AKA Mo Di as representative influential thinkers of each).

Are there influential non-Chinese/Indian/Arab thinkers who were also non-Muslin/Buddhist/Confucian? This results in a smaller list. There were surely many Persian and Central Asian thinkers from before the Islamic conquest whose names and works have been lost to us. Some we know of, but know very little of, such as Zarathustra (AKA Zoroaster), founder of Zoroastrianism. Others we know more about, such as Mani, founder Manichaeism. Shapur ibn Sahl (Sābūr ibn Sahl) was an influential Persian Christian medical writer. There were also many influential Jewish thinkers in Asia, such as Abu'l-Barakāt AKA Baruch ben Malka (who converted to Islam) and ibn Kammuna (who pushed his luck with writings that were viewed as anti-Islamic). We can also mention Jesus, who turned out to be highly influential. (Note that many of the influential Medieval non-Christian thinkers in Europe were Jewish too.)

The Asian Greek world also produced many thinkers, from early scientist-philosophers such as Thales through to influential early Christians (e.g., Paul).