Explicit surjectivity of Galois representations attached to abelian surfaces and $\operatorname{GL}_2$-varieties

Abstract: Let $A$ be an absolutely simple abelian variety without (potential) complex multiplication, defined over the number field $K$. Suppose that either $\dim A=2$ or $A$ is of $\operatorname{GL}2$-type: we give an explicit bound $\ell_0(A,K)$ such that, for every prime $\ell>\ell_0(A,K)$, the image of the absolute Galois group of $K$ in $\operatorname{Aut}(T\ell(A))$ is as large as it is allowed to be by endomorphisms and polarizations.