Hi so I have just switched over to the s9 and have had the same problem. Try this as it worked for me. The smiley face that appears in the message bar where you type is what you need to select. That will take you to the smiley you may want to use. Below will be the option the select gif. Select this and search by clicking on the magnifying glass. It appears that the gif button on the main bit is only for trending gifs or to locate ones that are commonly searched for specific keywords. It's all a bit silly and Samsung have definitely messed up. I hope this helps. I tried adding in screenshots but I can't seem to add images.
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