Following Radovan’s hint, Euler now checks for the number of parameters more carefully. This may have side effects on your programs. But must likely, you will just discover errors that you did not discover before. There are still ways to allow a variable number of parameters.
Moreover, Euler now can have different output formats for matrices and scalars. The defaults should be good for the user, as always. Use the recently introduce „longest …“ and „fraction …“ functions to format a single number.
I have tested the formulas on Wikipedia for the double pendulum. The animation can be watched on Youtube. The notebook is here.
For the Youtube video I used the nice Expression Encoder by Microsoft.