Enable creating a folder to categorize notes, Multiple similar notes can be stored here.

'Find' feature to detect words inside a note

on the startup screen "No Notes" message is visible for a split second

Add Tick mark (✔) feature for TODO list.
Add tick mark button which will on click add tick mark at the end of the sentence.

Auto-save only when the title & body content is not empty.

especially devices with round icon themes

If the keyboard is open then the user has to press back 3 times:

1. To close the keyboard.
2. To remove focus from the text field. (Disable this as it is unnecessary)
3. To finally go back.

Add text on the main screen when there are zero notes are available because the screen looks empty.
"Add your note" with an arrow pointing towards the "Add" icon

while editing notes if the user presses the back button then ask him if he is sure and give a warning that his data will be lost.

on click of add button, do a explode animation to present other features as a floating button above the add button.

Add button animation on click of a button and when the list is empty highlight "add" button

Add extra space at the bottom to solve it.

Add a search bar so that users can search notes by title.

When the user opens a note, show both times at the bottom end of the screen.

The widget feature will be a huge upgrade for the app and it will also be great to learn.

You can get to know more about this by using Samsung notes.

When adding a note allow the user to also add a reminder linked to it if needed.

Add sort by priority & remove sort by color.

The user might not understand the use of the filter section (Title, Date, Color), you need to add some title/heading to it, for the user to understand the use of it.
example: "Sort by", "Filter by"