You don’t need a daily standup
You don’t need a daily standup. But you do need to communicate often.
You don’t need formal retrospectives. But you do need to regularly discuss improvement opportunities.
You don’t need sprints. But you do need to break work down and deploy often.
You don’t need a sprint review. But you do need to iterate based on feedback.
You don’t need a scrum master. But you do need to assure the things above happen.
Note that there’s no universal ideal cadence for these practices. It will vary by team.
Ask, “are we doing these things often enough?”
Related: I’ve seen teams successfully rotate scrum master duties among the team.
Worth considering.