I don't think it's a good way to finally decide on a candidate, but a good starting point early in the screening phase.
There is a class of developers that exaggerates their skills to hope to catch attention. We had this for a frontend position recently where the candidate said he worked senior React developer at a few different companies in the last years. We usually ask for some code samples in the process and accept, that code from former employers can't be shared, but offer to give us a GitHub link or other public contributions to get an impression. If we then receive a GitHub account with half-ready React todo apps, it does t really support the senior developer story. Usually we then hear something like "just hire me and you will see how good I am", which from our experience often is enough to reject a candidate.
On the other hand, if we receive a few of from high school and can look around and see what the developer is learned in the years, it's a good indication to invite them for an interview.
The real comparison between different applicants is very complex though and can't be performed based on GitHub contributions, without excluding talented people on the way, in my opinion.
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