
If you have Windows 11 installed, then I would highly recommend use death.crafter's RainToaster; it is much more versatile.
RainToaster's only issue is Windows 10 system limit the notifications to one per session; you have to log off and back on to see additional notifications.

So, I created simple skin (based on other here) that will convert a date/time to a Timestamp and when the current time Timestamp matches, activates a Powershell script in a RunCommand measure and display the title, message, and an optional toast icon.
A preview of your toast using Window's Light and Dark theme colors will show when adding a new popup. A few notes...
Date/Time entries should be 2-digit and use 24-hour format time
The toast is strictly text, no option for images
The notification will be identified as a 'Windows Powershell' program post (I didn't try to change this)
The skin will run invisibly in the background, to check it !Refresh the config from Rainmeter
If a popup is set at a time in the future, a message will display giving details and offering to delete it and create a new one
Two skins are included, to create additional popup toasts simply copy/paste one of the current subfolders, rename it, and !Refresh-All
Hopefully it will be useful for quick reminders.