Unsure but think Sinner serve seem stronger and more committed (really leaps into serve, more body) and is using a small hop on BH.
They showed a graphic during the match on Tennis Channel tonight that compared Sinner's serve stats between his run to the Miami final and his run here in Toronto. Sinner was averaging 118 mph on 1st serves in Miami, and roughly 45% were landing within 2 feet of the lines. Here in Toronto, his 1st serve is averaging 126 mph and almost 70% are landing within 2 feet of the lines. So yes, his serve has improved in both pace and accuracy.
His first serve percentage is still too low
I agree in regards to the match tonight. His 1st serve percentage against Paul was a paltry 46%. He was fortunate to save as many break points as he did, and that he was returning well enough to break TP 5 times.
If Sinner serves with similar pace and accuracy tomorrow, but has a 1st serve percentage above 60%, he should not get broken. And he should be able to punish the DeMinaur serve on return. We'll see.