To add to this, a lot of people don’t see individuals with intellectual/developmental disabilities (IDD) as people. To them, they’re something else.
A person with IDD has all the same rights, including voting, as any other person. To reinforce that, many (or maybe all) states have their rights specifically codified (e.g., Florida Statute 393.13). To remove those rights, it requires a court order, just like it does for you and me.
In Florida, the supports for individuals with IDD promotes and assists them with the voting process, especially with getting to the polls to cast their votes!