The PSU that comes with the OPi5 bundle outputs around 5.3 volts when idle. This seems needed in order to compensate for voltage drop under load.
From my own measurements I noticed that the drop is quite severe and goes down to 5 volts under full load. Measured across the board at one of the USB ports.
If you have a common PSU that outputs "only" 5 volts then you can do the math for yourself and RKs in general are used to slight overvoltage.