My two cents
Most of the time I don't have to think about how much I need to pay research participants because most of my projects are:
Either internal, which means that research participants are the employees of the organisation and therefore they participate during work hours for which they are already paid.
Either use recruiting services like Testing Time, Lyssna or Pollfish that take care of defining and paying the incentives.
What the experts say
But if you have to define yourself what's a good incentive for research participants, the recruiting service "user interviews" has tried to answer this question with their report called "2022 Research Incentives Report" based on data from nearly 20,000 moderated and unmoderated research projects.
You'll find, for example, in this report this table:
Incentive calculator
With that data, they have also built a UX Research Incentive Calculator where you can answer a few questions and receive per email an estimate for a good incentive.
