First, download standalone Adobe Flash Player https://www.adobe.com/support/flashplayer/debug_downloads.html
Then click "File, open location (Ctrl Shift O on windows, Cmd Shift O on mac), then paste the URL where the URL goes. https://battlefordreamisland.com/5b/c.swf?path=5b.swf
Click "OK" and there you have it! 5b is playable in 2021.