Yes, but this is a “compact” only making it binding if a certain number of states agree - that is very questionable in its constitutionality.
Of course there is also the fact that there is no official “national popular vote” that is certified for anything.
It would be interesting if they did this and the result one election was that they caused a Republican to win against the wishes of their own state when otherwise they would have lost had the voters of their state gotten to choose their own state’s Electors. It would make it worthwhile to invest resources to run up the margins in states like Alabama, Mississippi, etc. in order to win the electoral votes of a state like Connecticut if they were to enact this absurd policy.
Not really. The constitution is clear, the legislature can assign and instruct their voter as they choose. There’s nothing about them making conditional rules based on the behavior of other states, or any other limitation.
Individual state votes are certified, everything after than is math. And remember they don’t even have to have voting. The legislature can just decide who to send and who to tell them to vote for.
That’s basically what will happen. Each party will focus on their stronghold state to run that margin up as far as possible. It won’t last long though, once a Dem stronghold state “goes” GOP because of the national vote they’ll go back.