Oh! It’s super easy! All you need to do is, using the online MakeCode browser, simply press the three dots next to ‘Download’ button in the bottom left corner. This is for just downloading the ‘uf2’ file. However, if you want to download it directly to some hardware, press the former. That should open a pop-up that kind of looks like this:
Next, select the device you plan to download it to. After you’ve done this, make sure your device’s screen is displaying the default boot screen, it should do this when plugged in. Finally, pair the device by pressing the three dots and following the instructions, press the download button one more time, and you’re all good to go! Let me know if you have any questions/trouble. 