About 6%, according to exit polls. The same percentage that voted against Bush in 2004 and Romney in 2012. Fewer than voted against Bush in 2000 (8%), McCain in 2008 (9%), or Trump in 2016 (8%).
Republicans supported Trump as much as or more than every other Republican Presidential candidate this century. I think you need to find a different narrative.
You appear to be making the other side’s argument actually. The only reason the Patriot Party might actually work to replace the GOP is precisely because the vast majority of Republican voters support President Trump, which is why a huge percentage of GOP voters are totally fed up with the GOP establishment backstabbing Trump and their own voters.
Although the Patriot Party might stand a better chance of winning over more working class, minorities, and anti-establishment types, for the most part the electorate will be the same. The main point of a new party would be a replacement of the party leadership and their priorities, allowing the base to have a party establishment that actually represents them. If the average Republican voter didn’t support Trump, then there would be no point in even discussing a new party, as a new party would have to prove that it is more successful than the obsolete GOP very quickly in elections to be worthwhile.