If you're looking to make plaza posts yourself, I would recommend investing in a stylus. While there are stylus designed for Switch, I can make decent-looking posts with an AmazonBasics one I got for Super Mario Maker 2. Definitely can't make top-notch art with it, but that doesn't matter because I am not an artist.
Note: The Nintendo Switch has an option to change touch screen sensitivity in the Settings menu. It can be set to Standard or Stylus. Setting it to Stylus makes it much more receptive to stylus input, much better for making posts.