You can't combine the two, because an endpoint applies exactly one geographic bias per request. That is why they are a union rather than separate options.
// Around a point, ranking bias only
const nearAmsterdam: GeoBias = { position: [4.9, 52.3] };
// Around a point, confined to 2 km
const within2km: GeoBias = { position: [4.9, 52.3], radiusMeters: 2000 };
// Inside the visible map area
const inViewport: GeoBias = { boundingBox: map.getBounds().toArray().flat() as BBox };
Where to look, as either a point with an optional radius or a bounding box.