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What are the proper compact connected subgroups of $Spin(n)$ of maximal rank where $Spin(n)$ is the spin group, that is, the universal cover of the special orthogonal group $SO(n)$?

In fact, I am only interested in the lowest highest dimension of a compact connected subgroup of $Spin(n)$ of maximal rank. I am not sure if this is an easier question.
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Proper compact connected subgroup of $Spin(n)$

What are the proper compact connected subgroups of $Spin(n)$ of maximal rank where $Spin(n)$ is the spin group, that is, the universal cover of the special orthogonal group $SO(n)$?

In fact, I am only interested in the lowest dimension of a compact connected subgroup of $Spin(n)$ of maximal rank. I am not sure if this is an easier question.