My ds is a bit older 6 now but has always been like that, doesn't play by himself and doesn't really like toys.
He loves lego but as he''s not great at playing by himself I set challenges eg go away and build me a car / dinosaur etc.. and he is getting better.
He loves anything outdoors so bike, scooter, football, basket ball, ping pong, trampoline.
We hAve also had quite a lot of success with sciency stuff bug collecting kits or volcano making sets etc..
Hé loves board games as well, we have the world monopoly where you just have to collect tokens for your passport, uno, some orchard toys stuff etc..
Other non play related stuff that have been a success were some super hero wall decals for his bedroom, a sort of kids survival kit (with torch, swiss army knife (blunt and useless so perfectly safe for him to carry) compass and little pack for them), a new sports bag for football, a large beanbag, joke stuff eg fake poo, the fart cushions, pots of sticky snot stuff etc.
I have absolutely no idea for this Christmas though so shall be following this thread to see what ideas other peagle have 