I answer as a long time dedicated player, a die hard loner and a self proclaimed digital pacifist :x
I mostly only play contact missions and races, because they provide me with fun without taking it away from others.
Heists do that too, but they involve too much loading times, inconsistency, noob-related failures and restarts, and the new ones even drag you into someones organization in a different lobby afterwards.
Survivals are boring and pointless and the few adversary modes that don't involve killing each other take years to populate.
Freeroam lobbies always have griefers or modders, so for someone who doesn't enjoy griefing, plays alone and relies only on randomness via on-call, contact missions and races are the only alluring options.
PvP could have been fun if not the unfair advantage in the form of mods every second player named 11232543456 has, or tryhard bullsh*t that forces you to downgrade graphics and imply macros to be competitive, if there were dedicated lobbies for pvp that say in their description "kill on sight, everyone is an asshole" or something, maybe i could extract some fun out of it but i really can't bring myself to start messing with someones affairs, killing random people blowing up their stuff sh*tting on their day, it doesn't bring me satisfaction but rather makes me feel like an asshole and that's all it does.
So i cling to PvE, and that aspect of the game, sadly, has very little room for a loner. no role play, no car meets, no off roading, only go on call and hope they don't kick me and hope they're not noobs and hope they know minimal english and hope they don't use OP rocket bullsh*t and hope the mission is on hard or the race is without catchup, and hope and hope and hope...
Most of the time ill be just driving around in an invite only session because those save loading times when bouncing from a contact mission to a race and back, its getting old.. Wish there was more PvE...