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.
Omg!! This happened to me this morning!! I have also never typed it, and I was in the middle of writing a huge emotional message in a Keep note when Gboard wanted to autocorrect "inhibits" with that. I was so gobsmacked that I carried my phone across the house to show my husband, but I didn't think to take a screenshot.
The last time it was trying to force wrong words on me, it was also words I had never used, but iirc it was very random slang kinda stuff, in the vein of "poggers" or "fleek" but not those.
I'm using an up-to-date Moto G Stylus (2023, 4g).