As much as you may dislike "fascists", you don't get to tell other people who they can or cannot send money to.
If I set up a monetary relationship between 2 entities and then I interfere with that relationship, this is called tortuous interference with contracts.
If you want to mail a check to these truckers, have at it, but GoFundMe is not obligated to collect money on their behalf. Here's another example, but not one Ron Desantis would ever care about - https://www.middleeastmonitor.com/20200131-gofundme-shuts-us...
A telephone company can't decide to give me a phone number then tell me who I can or cannot call. My ISP cannot tell me which websites I can or cannot access (without a court order). If GoFundMe allowed the convoy to open a charity drive, they cannot unilaterally close it and confiscate the money.