Can you clarify whether the SAMD21 M0-mini has a bootloader?

[SaulMagnusson]

For me on this board the Arduino USB programming port was inaccessible, and only the Native USB port was accessible, but sketches can't be uploaded that way in the Arduino IDE. So I agree with your first paragraph in the ReadMe that this board doesn't have a bootloader that will flash programs from the arduino IDE through USB and not through an SWD. But in your second paragraph you seem to say that the samd21 DOES come with the arduino zero bootloader installed. Is that true?

[RobertPatzke]

I use this board in Arduino IDE (not the original but with Eclipse/Sloeber, which does the same) as an Arduino Zero with native USB. No problems so far.

[tochinet]

I use Arduino IDE 1.8.19 on Linux today, and the board is recognized as 'Arduino Zero (Native USB Port)' and has a factory-loaded bootloader. So the answer is yes.