One way you can support him, or other prisoners, is to find out where they are and either send them cash as an inmate (be very careful about being specific in how you send cash because, of course, they make it extremely bureaucratic to discourage people from doing it - there are guides online).

Another way is to correspond with them by sending them letters of solidarity.

I know it's not as easy as donating to a GoFundMe or a Patreon account but having people go out of their way to tell you that they admire what you did and that they think you are a hero can really help buoy an inmate's spirits. Obviously cash helps an inmate access things - in some cases this is about health, hygiene and dignity (fuck the US for not mandating that all prisoners are provided with menstrual care products) and in other cases it's small luxuries that make doing time easier on the person.

There's also the opportunity to send books and magazines. Make sure you check what materials are permitted and what is banned though. Also try to send them stuff that they're actually interested in reading.