According to
https://sheldonbrown.com/tire-sizing.html#width, my 559-21 rim can have a 44-559 tire (up to 50-559). However, another website says that my rim can only fit 47/54-559 tires.
Is it safe to use a 44mm wide tire on a 21mm wide mountain bike rim?
Source: sheldonbrown.com
Source:
https://www.wtb.com/pages/tire-rim-fit-chart