There is a passive/ defensive mode that you can choose that will help mitigate "griefing" by other players and provide options / outcomes in the event you are killed.
To make a long story short though, if you you really want to avoid all risks, it's is best to avoid other players.....period.
- Don't choose missions / tasks that will automatically change your mode from defensive to offensive.
- When you first spawn into the map, the game tends to put you in regions with other players (IME). Pick a part of the map away from where you really want to be and then travel there by horse. IME, that usually helps limit the interactions you will have with others.
- Stay out of towns where other players are and if you have to go in, make your visit brief and give others a wide berth.
- If you can, play with friends in a posse. The old saying regarding "safety in numbers" applies here too. When you have several folks to ride with, other don't tend to mess with you as much IMO / IME but if they do, sometimes you can turn the tables on them and they will quit. ....o just ride out to another part of the map.
- Don't engage griefers unless you're will to pay the price of escalating the encounter.....repeatedly. If you use the defensive feature and advantages it gives you while just accepting your death. etc. by just escaping and moving on, there is little satisfaction for the offender. Remember....their sole purpose most times is to get a rise out of you by provoking a response.
As far as GTAV, there is no single player option like the one recently added where you can get play all of the missions, run all businesses, etc. with just you and/or friends. However, the "MTU exploit" does work like it did for GTAV but just not as well. .....at least the last time I tried it about a year or to ago. It helps force you into your own session but it's inconsistent. .....and any missions that lead to you leaving the session can dump you back into a populated server once done, etc. You can also be kicked out of the session from time to time. Not really worth it IMO.