One of the most pro-Republican states is Wyoming, state population around 581,000 in 2020. If we consider Trump voters as a proxy for people who might want to secede, we have about 235,000 people who voted for Trump out of about 427,000 eligible. That's about 55% of eligible voters and 40% of the whole population. Even if secession were legal, it would be unjust to let a state secede with only 40% support.

A more viable attempt at secession might look like: perhaps a new Hawaiian independence party forms with massive (>80%) and sustained (>20 years) on-the-ground support, with all federal representatives coming from this party. Eventually this party might convince the federal and enough state governments to support a constitutional amendment recognizing a specific independence referendum. That's very theoretical but I hope illustrates what actual secession might look like.