Whether via browser or app, when I try to select this reason the only choice offered is the local Meta. If that's deliberate, the language inviting us to choose, and indeed that whole step, are misleading/redundant. If it isn't, could we get this fixed someday?
Each site has its own list, which may be as small as its per-site meta. This is by design. You can't move to an arbitrary site, only to those the site admins have decided are typical targets.
However if you are sure it belongs somewhere that is not on the list, use an Other flag and explain to the moderator where you think it should be migrated to.