The yellow tape is for sealing, the molded strip makes a shape that's like UST and helps the tire seat. You should use them both.
My first tubeless setup a few years ago I did with two rounds of Gorilla tape (which fulfills both functions) in a very old wheel. That worked okayyyish. More recently with "real" tubeless rims and thin tape it's been much more satisfactory.
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Genesis 49:16-17