For passing mathematically the peak or passing from an inflection point in load-deflection curve or moment-curvature curve applying original Newton-Raphson method is not enough, other method targeting a constant force greater than the peak load, fixed to reflect back the tangent to the curve at any point are used, for this the modified Newton-Raphson method or Riks method cab be employed. Numerically for passing the peak or inflection point you can not apply the imposed force ( i.e. force based method "FBM") in this method the force can not pass the peak. You should apply the imposed displacement (i.e. Displacement-based method "DBM"), in this way displacement increases all the time to failure, i.e. for this, the force-based method (FBM) should be forgotten and the displacement-Based method (DBM) should be used. Based on my proposed methods of simulation of RC members, that you can find them by googling, I have even proposed a strain-based method (SBM) for finding the moment-curvature in the sections and then by applying the double integration of curvatures or by applying an Elastic-plastic approach you can find the deflections of the RC member and perform the load-displacement curve. Briefly, by apply the DBM or SBM you successfully will pass the peak. Follow these concepts when you apply the software. good luck.

Concrete is defined using Concrete damage plasticity model (CDPM), the degradation after peak can be witnessed.

Please

1-define the Concrete damage plasticity model (CDPM) and therefore the stiffness of the over stressed elements will be reduced which leads to the reduction of the overall stiffness of the structure and passing the peak to the descending part of the load-displacement curve.

2- Use the displacement loading NOT force loading.

3- Set the convergence criteria properly enough

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Please note also that do not have to draw the descending part to pick the peak load.

If the load continues constant without increase, this means that it is the peak (limit load analysis) ...

However, drawing the descending part is more professional and reliable because you are doing failure analysis