What's the difference between "Apple ProRes MXF OP1a" 、 “DNxHR/DNxHD MXF OP1a” 、 "MXF OP1a"?

It's formats and codecs ... MXF OP1a is a format, and formats are often called "wrappers". They are a format to contain other data ... in the form of codecs. Many formats can "wrap" several different codecs.

ProRes and DNxHD/R are codecs. A codec is a specific schema for encoding video or audio data. Cineform is also a high-quality intraframe codec like ProRes and DNxHD/R. Meaning that all frames are complete data-sets for that frame.

As opposed to say the long-GOP (group of pictures) format H.264/H.265, where there are only complete or " i-frames " every  9-30 (or even more) frames of media. In between are simple data sets of pixels that 1) have changed since the last i-frame; 2) will change before the next i-frame; or ... 3) both. Long-GOP media is fast to write to card in-camera because of the specialized chips included to do that parsing of data. They are Hades on computers for playback because of the demands on the CPU/RAM subsystems.

Learning about formats ... and codecs ... is really necessary to understand how to work and delivery the appropriate quality image.

Neil