What's the largest REG_SZ value that Regedit can edit?
Solution 1:
The largest string that can be displayed in the Regedit's textbox has a length of 43679. beginning with a length of 43680, the textbox will appear to be empty. (Windows 10 21H1, if that matters).
And I say "appear", because the value is actually still there. You can press Ctrl+A and Ctrl+C in order to copy it into the clipboard. And you can also copy a text into the clipboard and paste it back to Regedit and accept it.