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MRTK 3 is not a new version of MRTK 2. MRTK 3 is a new generation of Mixed Reality Toolkit. Its namespace structure and included APIs are different from MRTK2. For this official tutorial, it currently only works with MRTK 2 and has not been updated for MRTK 3. Currently, there is also no easy way to update a project from MRTK 2 to MRTK 3. If you need the features in this tutorial, you may need to manually rewrite the relevant code yourself with MRTK 3.
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