Proof. Let All objects in are supported on a closed subset of consisting of finitely many -orbits by condition (FO) and are pointwise pure Tate using condition (PT) and Proposition 3.21. Now and are constructed from the objects in by a finite combination of taking direct summands, finite direct sums and triangles. Hence and are also supported on a closed subset of consisting finitely many -orbits and are pointwise mixed Tate. Now the statement follows from Proposition 3.20. ∎
Original source: arXiv:2109.00305v2