I am of the opinion that the best way to stop the Popular Vote effort is to have 26 States pass state constitutional amendments that define how the electors will be decided for each state. As long as the states do not pass amendments supporting the Popular Vote, and if 26 states enact such amendments, there will never be enough states to pass the Popular Vote.
Personally, I would prefer each state pass amendments to follow the district system - each district awards it’s elector to the candidate that wins 50%+1 vote, run off if no one gets 50%. The two “senator” electors get awarded - 1 to the candidate that wins the most districts and 1 to the candidate that wins the most overall votes in the state. Gov decides ties in either of the senator electoral awards.
I prefer this plan as it maintains the Republic nature of the US and disenfranchises the fewest possible voters.
The present Electoral College system discourages cheating in those areas where cheating would most likely succeed.
Once a majority of Californians decide that the Democrat should be President, it does the Democrat no good whatsoever to steal more votes through fraud in California. That is a good thing.
At the same time the place where cheating might be effective would be those where Republicans have nearly as much political power as the Democrats and thus might be expected to be able to detect or prevent such cheating.
I am reminded of a report I read some years ago that King County in Washington reported vote totals which greatly exceeded the number of registered voters.