For me, a technology itself isn't a red flag. Not being able to explain the reason for choosing one approach over another is a big red flag.
Or if the reason is "I want to try this new thing" and not "Our standard production stack won't work for this because (valid technical reasons)" that's a huge red flag.
Or if the reason is "I want to try this new thing" and not "Our standard production stack won't work for this because (valid technical reasons)" that's a huge red flag.