If it's interesting enough, I will read anything regardless of how many chapters are uploaded. But I do prefer at least 20 chapters assuming the bare minimum of ~1500 words per chapter. On the other hand, if a story already has high 100s of chapters before you start reading it, it can be discouraging.
And of course, the "Completed" tag takes precedence over actual length - so a completed story (one-shot / short story) with 1-5 chapters is better than an ongoing one with 50, especially if the updates are infrequent and/or there are other red flags, like the author having multiple unfinished stories.