SAMD
SAMD21 (M0) is tight; SAMD51 (M4) is the comfortable one. Many boards in this port look like Adafruit Feathers. Flash is usually UF2 via a bootloader. Docs: samd quickref.
What to expect
Pin, PWM, ADC, I2C, SPI, UART, Timer, RTC. No on-chip Wi-Fi — add an ESP coprocessor or use a different port if you need a radio. CircuitPython is common on the same hardware; MicroPython firmware is a different UF2, not a drop-in replacement for a CIRCUITPY drive workflow.