How do I set an alarm 🚨 in the reminder app please

That's not necessarily true. Until recently, people were able to set "future alarms" (aka alarms greater than 24 hours in advanced) on reminder to help them remember certain upcoming tasks. It was helpful because you could customize when the notification would come up and customize it further. I'm guessing that feature was removed for some reason which is a huge let down to those of us who were used to utilizing that feature.

You can set an alert with a reminder for a future date, that is not an "alarm".

You don't set alarms in the reminders app, you set alarms in the clock app.