The https://progress-bar.dev/ site lets you create images that display percentages or similar numbers in bars, and you can insert them into md files with markdown.
For example,  will give you this:

You can include words in the bar:

There’s other examples at the link above.
I’ve just tested in my Obsidian files and it works there.
The alt text and title text (“progress 28%” in my example) aren’t strictly needed for the image to appear but either would allow you to do text searches for specific progresses, and the title text would appear on-hover if that were important to you. The alt text would allow you or others to understand the image when using a screen reader.
[this is alt text](http://example.com/image.png "this is title text"
You could standardise on using percents in increments of 10 to make it easier to search for notes at a specific level of completion (i.e., use 10%, 20%, etc, never 16%).
Using different words would allow you to have two or more grades/ratings for each note.



