This simple FastAPI script:
from fastapi import FastAPI
from geojson_pydantic import FeatureCollection
app = FastAPI(
title="Test geojson-pydantic",
version="1.0"
)
@app.get("/{dataset}", response_model=FeatureCollection)
def get_dataset(dataset: str):
raise NotImplementedError
Creates this result in /docs:

See here for a simple project.
Edit:
- fastapi==0.104.1
- pydantic==2.5.1
- uvicorn==0.24.0.post1
- geojson-pydantic==1.0.1