You can spell. Very good. Now point out to me where the Constitution says that Congress has only powers e-x-p-r-e-s-s-l-y granted. You can't, because it doesn't. Congress has implied powers that can be identified by a realistic reading of the Constitution. And one of those powers reserved to the United States Congress is the power to approve secession of states.
BRAVO SIERRA! The United States (i.e the federal government) has NO reserved powers, it only has delegated powers, and can only enact laws PURSUANT to those DELEGATED powers - that's why we have a WRITTEN Constitution [I can CAPTITALIZE too!]
The states have all the powers NOT DELEGATED to the federal government [please cite the express delegation of the federal government to prohibit secession], and the powers NOT PROHIBITED by the CONSTITUTION [not by congress, the President, or the Supreme Court - again cite where secession is prohibited].
So you resort to implicit powers. Too easy to refute, if the states could join/accede unilaterally, then implicitly they can secede unilaterally. No principal needs to ask their agent for permission - the agent serves at the will of the principal.
That isn't what Hamilton told us in Federalist 84:
I go further, and affirm that bills of rights, in the sense and to the extent in which they are contended for, are not only unnecessary in the proposed Constitution, but would even be dangerous. They would contain various exceptions to powers not granted; and, on this very account, would afford a colorable pretext to claim more than were granted. For why declare that things shall not be done which there is no power to do? Why, for instance, should it be said that the liberty of the press shall not be restrained, when no power is given by which restrictions may be imposed? I will not contend that such a provision would confer a regulating power; but it is evident that it would furnish, to men disposed to usurp, a plausible pretense for claiming that power. They might urge with a semblance of reason, that the Constitution ought not to be charged with the absurdity of providing against the abuse of an authority which was not given, and that the provision against restraining the liberty of the press afforded a clear implication, that a power to prescribe proper regulations concerning it was intended to be vested in the national government.* This may serve as a specimen of the numerous handles which would be given to the doctrine of constructive powers, by the indulgence of an injudicious zeal for bills of rights.
*This is exactly what you are doing with your argument about the Tenth Amendment, sovereignty, and the People's power to secede.
I told you before, and I repeat, we aren't talking about the implied power of the White House housekeeper to order tea cozies with the proceeds of a congressional appropriation. We are talking about the highest questions of politics, and there is nothing implied, nothing interlined, nothing that you can invoke by necromantic skill that will allow you to infer such a power of the Congress. Powers like that are all delegated and listed in Article I. If you don't see it there, quit telling us it exists, because it doesn't.
And to get down to cases, you don't really mean that Congress has the power to forbid States to leave the Union, do you? You mean Abraham Lincoln.