There is a safe way and a risky way to do this, and the risky way is the one most people reach for first.
Cropped pixels are deleted. They are not in the saved file and there is nothing to recover. That makes cropping the most reliable way to remove something, and it should be the first choice whenever the sensitive part is near an edge.
Blur is the risky habit. Blurring is a mathematical transformation of the original pixels rather than a deletion, and blurred text has in practice been recovered, particularly short predictable strings like account numbers. A solid block removes the information instead of scrambling it.
Check the whole frame, not just the part you were thinking about. Tab titles, notification banners, a name in a sidebar, an email address in a header. The detail you forgot is the one that gets shared.
Less than people assume. Blurred text has been reversed before, especially for short predictable values. A solid block is safer.
No. Those pixels are not in the saved file.
No, which matters given what screenshots usually contain.