Is no social media a red flag in dating?

You won't know until you ask.
Just because you think it's weird doesn't make it weird. It's impossible to judge someone's compatibility with you based on narrow criteria like this one.
If you believe that social media is your requirement to date someone, then not having it would be a red flag.
But if you think there's something wrong with them because they don't have social media, that's probably an unfair judgment.
In that case, ask that person why they don't have social media. They might have their own reasons that have nothing to do with actual compatibility.
Don't rush to judge people that you might be dating. But if you're curious what their motivations are, ask them.
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