The Texas Legislature has an absolute right to appoint 40 Trump Electors, they could do that right now in fact although those Electors could not vote until December.
Nothing NY has done or could do impairs the plenary power of appointing Electors for Texas that belongs to the Legislature.
Based on the CNN article that I posted in the link (which you are free to dispute, given the source), the "plenary power of appointing Electors" has limits.
Yes, the legislatures of the several states have the plenary power to choose the method of selecting Electors. They exercise this power by means of their legislative process, and the executive of the state signs the bill into law just like any other. Once that bill is passed into law, the state legislatures are obligated to follow those laws until either: 1) some trigger in the law gives the state the power to immediately respond (like failing to certify in time for the Electoral College safe-harbor date), or 2) the legislature changes the law again via its normal legislative procedures.
Plenary power does NOT mean the legislature can simply waive away the existing law and act unilaterally if it wants to. To do so would make them no different than kings.
If the Texas legislature wanted to do as you suggest, they will have to call a special session to change the existing law. What would that new law be? Would it be that the state of Texas hereby appoints only Republican Electors and all elections for Electors from now on are hereby canceled? Would it be that the legislature of Texas will assume the vote for Electors and all elections for Electors from now on are hereby canceled? Or would it be that the election for Electors for the year 2024 only is hereby suspended and the state Legislature will choose the Electors directly?
-PJ