No, we don't. This is not an yes/no answer. This is the type of question that should be answered in terms of confidence intervals.
> right wing tweets actually got promoted more
In relation to what? What is a "right wing" tweet? What is a "left wing" tweet?
E.g, if the algorithm is focused on filtering out disparaging extreme messages, and it ends up filtering X amount of "non-extreme right wing content", 3X of "extreme right-wing content" and 5X of "extreme left-wing content", it satisfies the claim that "it promotes more right-wing content" while also silencing conservative voices.
The advantage of the right in social media news sharing: https://academic.oup.com/pnasnexus/article/1/3/pgac137/66516...
Upenn article summary: https://penntoday.upenn.edu/news/Penn-research-Twitter-gives...