There are activities for anyone who is interested. (would "that" also be grammatically correct?).Welcome to the forum, verkat.
Please always give us a complete sentence to consider.
I think "who" is more natural. However, you could also use "that". You could also say "for anyone interested".There are activities for anyone who is interested. (would "that" also be grammatically correct?).
With "that is", I agree. However, in casual everyday BrE, you'll hear "for anyone that's interested".I don't think I've heard of "for anyone that is interested".
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