Let them.
If they want to create a MAGAverse, so be it. We can build a wall to keep the feral Trumpers out. We can set up a repayment plan so Red states can pay back the federal dollars they've been leeching. We can fine them for every gun that is found illegally across the border. They can reimburse blue states for FEMA relief if they want to deny climate change. They can be ravaged by the next pandemic of they don't want lockdowns or vaccines. The voters in those states don't face real consequences (outside of being financially poor and having borderline 3rd world health outcomes) from their idiotic voting. Give them what they want.
Consider that 9 of the 10 poorest states are Red, and 20 out of the poorest 25. Blue states are subsidizing their existence. So, by all means, secede. If they don't want the tyranny of the federal government, give them what they want. I don't want blue state tax dollars to subsidize them anymore.