Because I'm working, everything goes into works Outlook TBH, but my life isn't that exciting so if I pop 'leave; in there I know what it is. I don't have many 'social' appointments...boo hoo !
My life is not exciting either, but: dentist, hairdresser, annual leave booked, tradesman coming, annual boiler service, vet appointments, if friend I usually meet is away or home, overtime I promised to work (better show for the shift!) ... deadline to pay off the interest free credit card
Google calendar on my phone only for me.
However, sometimes I use a What's App conversation for reminders, like for when a tradesperson is coming (because they messaged me) and for how much the job will costs.
For some stuff due to happen short term, I just let the automatic text/emails remind me, without putting them on the calendar.