Hello,
I would like to know if using the sample assets (specifically those from the URP sample scene) could be used as grounds for academic dishonesty (plagiarism), given the explanation that the assets (for instance the helmet, table) were taken from the URP sample scene.
That would be a question for your school/instructor and not for us.
It will depend on the policy of the academic institution, and where they are being used (allowed asset use would be very different on an art course assignment compared to a programming research project for example), but in general, plagiarism in this kind of case would be passing off the assets as your own creation. A typical way to treat this would be to reference the assets, and describe how they are used, so it is obvious what is not your creation.