或?是: What could the mysterious word be
yes, it is 或者是.
From the meaning, 或 alone is alright here. 或者 and 或 means the same in Chinese.
Sometimes the choice between 或者 and 或 is related to the rhythm of sentence.

然後讓更多的德國人[pause here]或者是歐洲人[pause here]認識這個琵琶。

Both 更多的德國人 and 或者是歐洲人 are with six characters/syllables.
Another reason is a historical one. 或者 is commonly used in Classical Chinese as the start of a short sentence (complete or incomplete in English sense). 「或者是歐洲人」is treated as a short sentence.
If you want to dig a little bit deeper about 者, here is my explanation.
者 can accept anything before it, any word, any phrase. It is a marker referring to anything prepended to it.  You might perceive it as &quot;one that&quot;. 或者 is &quot;one that is alternative&quot; or &quot;alternative one&quot; and it simply means &quot;or&quot;.