> 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.