This has been happening for a while now. Whenever I go to make a reminder for a specific time, the time disappears and the notification doesn’t pop up. My mom’s reminders work and she has an older iPhone than me. I have watched multiple videos and read multiple articles but nothing has worked. Someone please respond because the Reminders app is how I basically run my whole life.
iPhone XR
Hi PrestonElliott,
Welcome to Apple Support Communities. Let's try deleting the Reminders app, restarting your iPhone, and installing it again to test the issue. This will clear any corrupted data of Reminders from your iPhone.
Delete apps on your iPhone, iPad, and iPod touch - Apple Support
"How to delete an app
Touch and hold the app.
Tap Remove App 
.
Tap Delete App, then tap Delete to confirm.
Keep in mind that some built-in Apple apps can't be deleted from your device, so you might not see the option to delete an app. Here’s a list of built-in Apple apps you can delete from your device. If you can't delete an app that's not made by Apple, disable parental controls, then try deleting the app again.
If you touch and hold an app from the Home Screen and the apps start to jiggle:
Tap the Remove icon 
in the upper-left corner of the app.
Tap Delete App, then tap Delete to confirm.
Tap Done."
Restart your iPhone - Apple Support
"Press and hold either volume button and the side button until the power-off slider appears.
Drag the slider, then wait 30 seconds for your device to turn off. If your device is frozen or unresponsive, force restart your device.
To turn your device back on, press and hold the side button (on the right side of your iPhone) until you see the Apple logo."
We hope this helps.
Cheers!
Timed/Scheduled Reminders Aren’t Working iOS 15
