It is just a public statement of support. There are only consequences to the extent that people care about/respect the opinion and judgment of the person giving the endorsement.
In this case, it’s valuable to RFK Jr in so far as individuals listening to Joe Rogan either think Joe has good insights into who should be president, or just want to be like him and will vote the way they think he will vote
Not a big gamer, myself, but it seems like Valve has done a lot of work to make many (most?) Steam games run well under Linux.
Drivers have come a long way, and a lot of things just work, but it can definitely depend on what hardware is in your system.