Texas doesn’t have to accept it. But Texas might gain by it. Right now Presidential candidates ignore Texas because its vote is a foregone conclusion.
The Constitutional grounds are that each state is free to appoint their Electors any way they see fit.
Ohio could have a convention of PTA Presidents choose its Electors and there’d be nothing to say about it.
It is one thing for a state to decide to do something stupid like this, but quite another to make an interstate pact to vote as a block.
As if the elections had no effect? This cannot be constitutional.