You could try the Scapple beta and see if that works better. I recall we might have changed a few things with auto-size, and overall the code for that update is revised. macOS 11 should be fine (we support back to 10.15 officially).
Also, to make sure I understand, it works normally if you paste the English “word” into a note and click away, but not Chinese characters, or does it never work if that is your keyboard input method?