Looking at the underlying study, this isn’t evidence of bias. It’s evidence of correlation between Republicans and negative sentiment.

If you look at the sentiment for public figures given, the bottom one is, for example, Brett Kavanaugh. Well, he was credibly accused of sexual assault during his confirmation hearings, which was a huge deal at the time. Someone with that on their record will probably be read as negative, but, I mean, not the editors’ fault!

When it comes to politics and studies... We all should know by now to research those sources too, right?

"The Manhattan Institute for Policy Research is an American 501(c)(3) nonprofit[5] conservative think tank."

It is a report generated by this conservative organization (that presumably gets donations from many other conservatives). Is there a chance that the report itself is suspect?

"Bias" here is just sentiment analysis. The report (from a conservative think-tank) is not about factual errors. Plus, the effect they find shows only for US politics, where there is really not much of a "left".

> Findings show that Wikipedia entries are more likely to attach negative sentiment to terms representative of right-leaning political orientation than to their left-leaning counterparts

Is that a bias or just reality?

Right leaning politicians in the US include people paying underage girls for sex, people screaming about "Jewish Space lasers", people obviously stealing money in plain sight with crypto pumps and dumps, people running away from responsibility, people getting caught engaging in sexual acts in public, and on and on and on. Their left-wing equivalents are... extremely mild by comparison. What, some run of the mill corruption and sexual comments that resulted in resignations?

If go past "right wing is associated with more negative things", and look into what those negative things are, you'd realise it's just reality. Just because there are two parties and two categories of political leanings doesn't mean they are somehow equal.