It's literally replacing every single swiped word with the "soft n-word." Every word, including things like "the" and "top".
This is happening to me right now on gboard, most updated version of Android, running on a Pixel 5. This has happened before and y'all gotta take my word for it that I haven't done anything to teach my phone that that's what I want to type.
someone played a prank on you by creating text shortcuts. go to the keyboard's settings and check.
Nothing in my keyboard settings, nothing in my personal dictionary. I keep all autocorrect turned off anyway.