Are there apps that can read blacked out texts?

It depends on the type of image, the app, and how it was made.

If you have a full copy of the Adobe PDF maker (not just the reader) and the person who made the text saved it as layers (i.e. didn’t flatten the file) then you can unmask the blackened layers. The problem is that most people who do this are smart and don’t make that mistake.

If the document is a JPG or GIF or other image file – then the answer is NO.

So it depends.

Ask the CIA.

Occasionally text is blanked out by changing its type color to match the background.
Try to change either the text color or the background. You might get lucky.

An image or scan of an original document that had a physical black marker applied, might be possible to read using an image filter, if there are subtle differences in the color data where the text was, that might not be normally visible, but the image filter software might be able to highlight so it becomes visible. Probably not, but maybe.

If it’s some overblown word processor format that was designed without security in mind, like Microsoft Word, then the history of edits may be saved in the document. I’ve seen Word documents that include EVERYTHING EVER DONE TO THE DOCUMENT SINCE IT WAS CREATED, including earlier drafts or completely different letters or compositions, when the user took an existing document and re-used it to make later documents.

Sometimes if something is blacked out with a market, you can hold it in the light and see the original font shine through.