Hey there, LuisTSantos.
After reviewing your post, it appears that you're having a problem creating Reminders using Siri to set them up. The Reminder shows, but it isn't saved to the app, and we're glad to help with this.
Update your iPhone, iPad, or iPod touch -- Make sure your iPhone is up to date. iOS 14.0.1 is the current version. If it needs to be updated, be sure to create a backup before proceeding: How to back up your iPhone, iPad, and iPod touch
Use Reminders on your iPhone, iPad, or iPod touch -- If you have more than one Reminders list, go to Settings > Reminders > Default List to what list it’s being saved to. If it wasn’t set to the one you expect, check the list.
Use iCloud.com -- You also mentioned using iCloud to sync your Reminders. See if they're located in iCloud.com/reminders.
Let us know how that goes.
Take care.