There's no such thing as entropy depletion, but there is such a thing as an insufficiently seeded CSPRNG - which means that /dev/urandom is not secure by design

There's no such thing as entropy depletion, but there is such a thing as an insufficiently seeded CSPRNG - which means that /dev/urandom is not secure by design: it does not protect you against that failure mode, and in fact people rely on fragile hacks implemented by distributions to try to seed /dev/urandom properly as soon as possible in the bootup sequence. These hacks could easily break if somebody does not know exactly what they're doing while touching the boot sequence. /dev/random is also stupid, but it does protect you against that particular failure mode.