Yes, it is compatible with Canon EOS R and EOS M mirrorless systems when used with the official EF-EOS R or EF-EOS M mount adapters.
Yes, the STM (Stepping Motor) provides smooth and quiet continuous autofocus, which is essential for high-quality video recording without motor noise.
No, this lens does not feature weather-sealing. It is not waterproof and should be protected from rain and high-humidity environments.
The Canon EF 50mm f/1.8 STM uses a 49mm front filter thread.