Well, Jesus did say in prayer >
"Abba, Father, all things are possible for You. Take this cup away from Me; nevertheless, not what I will, but what You will." (in Mark 14:36)
So, He does say in prayer for God to take away His cup. It is something Jesus does not want to go through, I can see. So, yes ones can say He was speaking against God's will and so that was sin. And yes there are ones who claim that Jesus was "fully man" and so He was capable of sinning.
But it is written >
"For we do not have a High Priest who cannot sympathize with our weaknesses, but was in all points tempted as we are, yet without sin." (Hebrews 4:15)
So, if it is an object of faith that Jesus never sinned, how might we explain that He prayed for our Father to remove that cup from Jesus?
One thing > Jesus says "the Father who dwells in Me does the works," in John 14:10. So, our Father in Jesus did the work of having Jesus pray that prayer to have our Father take the cup away from Jesus! And Jesus says, "He who has seen Me has seen the Father," in John 14:9. So, Jesus was expressing something which represented our Father . . . how our Father did not want Jesus to go through all that, but it was necessary.
One thing I think of is how Jesus was not only concerned about the suffering, but He was caring about how those evil people would be so degrading themselves with Satan while doing what they did to Him. He did not wish to experience them so hating Him, when He is so about love. So, I see, part of His not wanting that was how He deeply cared for those evil people.
And we see another example, maybe we could say, of how God does not want something which is going to happen >
He is "not willing that any should perish," we have in 2 Peter 3:9. But even now ones are perishing.
So, yes there are realities that God does not want. And Jesus did not want to so suffer and be so exposed to personal hatred of those who tortured and murdered Him, but He did what was needed . . . so that people do not perish.