What I needed for the hard one were a 2sk(R3C4<>3), an x-wing(R4C3<>3), a disc nice loop(assuming R1C1=2 leads to contradiction, so R1C1<>2=5) and another disc nice loop(assuming R2C7=7 leads to contradiction, so R2C7<>7=5).

Like to see a solver output to compare if it can be done easier.