Does agreeing with a potentially harmful or biased statement on social media have the same impact as saying it yourself?

Yes, it has an impact on myself since I refuse all sources of hatred on all groups.

yes as it may encourage others especially (if you have a big social media presence) to agree with you, and believe these things

Agreeing with a potentially harmful or biased statement on social media may give the impression that you support that statement/video, even if you don't. So it's important to think critically before engaging with thosr kind of things.