The NPS question, by default, supports up to 10 rating scales and cannot exceed that limit. However, as an alternative, you can use a Matrix Multipoint Scale question to add more than 10 rating options. After collecting responses, you can apply the "Custom Scoring Model - NPS" to define promoters, passives, and detractors based on your scale.
Screenshot for reference: https://prnt.sc/eYlkMvfFZDrJ
Kindly check help files for more details:
Matrix Multipoint Scale Question: https://www.questionpro.com/help/matrix-multipoint-scale-question.html
Customize Mean Calculation: https://www.questionpro.com/help/customize-mean-calculation.html