On nonemptiness of Newton strata in the BdR⁺-Grassmannian for GLₙ

We study the Newton stratification in the BdR⁺ -Grassmannian for GLₙ associated to an arbitrary (possibly nonbasic) element of B(GLₙ) . Our main result classifies all nonempty Newton strata in an arbitrary minuscule Schubert cell. For a large class of elements in B(GLₙ) , our classification is given by some explicit conditions in terms of Newton polygons. For the proof, we proceed by induction on n using a previous result of the author that classifies all extensions of two given vector bundles on the Fargues–Fontaine curve.