R
As a Scrum Master, you can do your best. But your best might not be enough. I have seen people that were so distrusting and obviously hurt by their former bosses and management strategies of backstabbing, blaming and favoritism that they could not let go of those experiences and bring up the initial mental investment of extending a minimum of goodwill and trust to a new beginning.
Teamwork is all about trust. "I need help" is a basic, fundamental sentence in team work. If you cannot find the courage to say it, because you have been experiencing for years or maybe even decades that this sentence only causes you pain from people that will exploit your weakness to it's fullest to gain something, then teamwork is impossible.
I have had the fortune of witnessing this first hand. We had a big company with ~50 developers and we transitioned from command and control to multiple Scrum teams. Of the new formed teams, all under the same conditions, under the same Agile Coach and same line manager that did not interfere, some worked great, some just worked okay and some just didn't. Or only formally, but not as a real team. As a Scrum Master, you can educate and offer the opportunities for teamwork, but they have to be taken. You cannot force teamwork and trust on someone. If they don't put out a little bit of good will and see what happens if they are "weak" and ask for help but instead stay in their defensive shell, there is little you can do.
You are a Scrum Master with a potential team member, not a psychologist with a patient. You can lead by example. You can offer opportunities. You cannot make people take them. And you certainly don't have the skillset to fix people's trust problems.
As a step forward, if you find that your offered opportunities are not accepted, find out what the problem is. Do they not trust you? Then you need a different Scrum Master. Do they not trust each other? Then you need maybe a different team composition if you have multiple teams, or you need to replace those people that aren't trusted. Do they not trust the whole process, because they have been burned by the company before? Then there is little you can do.
Make a list of opportunities you offered, explanations you gave, workshops you had, teamwork games you played, demonstrations to show that Scrum and teamwork produce better results. Go through it yourself and think about other opportunities. Talk to your team about it. If you cannot find a solution, talk to your manager about it. Scrum is not a silver bullet. It works through team work, it cannot enforce team work. If you find member(s) on your team to not be team players despite your best effort, you need to switch them out, as you would in any other team.