A reminder can help you notice a birthday or an important appointment. It cannot tell you exactly what that date means to the person this year.
Before sending an automatic greeting, check the current context. Is the person celebrating publicly, keeping the day quiet or facing a complicated milestone? If you do not know, a modest message may be more appropriate than an elaborate assumption.
Specific attention can make a greeting personal: ‘I hope you get some time for the walk you’ve been looking forward to.’ Use a detail you actually know and that is appropriate to mention.
For an appointment or event, avoid requesting an update as though the reminder gives you a right to the result. ‘Thinking of you today’ can leave more room than ‘Tell me immediately how it went.’
It is also fine to use a reminder as a prompt to decide whether to write at all. The right action might be a call, a practical offer or simply respecting a preference for privacy.
Let the tool handle remembering the date. Keep the decision about the message connected to the relationship. A calendar can bring the moment to your attention; the meaning of the response still deserves your judgment.