Is there any way to limit editing in Google Docs?

What you can do is make the table on Google Sheets and then put it in the Google Docs,

Here's how to do it on google sheets...

First, click on the cell that you want to limit the characters in

Then click "Data validations"

Then go to Custom Formula

And input "=(len($C2)>=500)*(len($C2)<=2000)" this is for cell C2 change "$C2" to whatever cell you want the formula to work in

This formula is basically making the input great than or equal to 500 and less than or equal to 2000

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And if you were wondering how to add a table from google sheets all you have to do is go to "insert" than "chart"

Then press "From sheets" to get the table from google sheets into google docs

There isn't a built-in feature that does that you might use a custom sidebar to hold client-side code to constantly poll the document to count the character of the active Google Docs element by using Google Apps Script or use a Google Docs add-on that does that if its exists.