A well-placed flyer can reach the eyes of thousands of people per day, regardless of which social media platform they use, if any.
If you make a flyer for an event, share the file online and encourage others to print them out too.
Before sharing, remove the metadata with Scrambled Exif on Android or Metadata Anonymisation Toolkit on Linux. Sending a copy to a friend? Send it over Signal.
I’ve made stencils before, but I was wanting a decent pasteup option too, just because they’re faster to put up and less sus than spray paint. Maybe leave a tiled flier design to run overnight and then cut it apart or something.