If you have an iPad, there's an app called iReal Pro with loads of lead sheets that add in some accompaniment (drums, guitar, etc.) so you can "play along" as well.
It's also available on Android, and it's a one-time payment, no-subscription app. Easily one of the most valuable music purchases I've made.
The reason is that copyright only covers melody and lyrics, not harmony. So the harmonies are essentially public domain.
And a lot of natural variation has been elided with these tools, a lot of jazz classics I'm pretty sure didn't really have a "standard" version until after the real book took over; different fake books were popular in different cities and so there was regional performance variation that we don't see much of anymore.
There are probably novel issues introduced by the ireal fakes but a lot of them are the same problems my grandfather was observing as a young working musician when the real book became so dominant. They are extremely real downsides of these tools though.
A looper pedal and an AirStep Play are helpful antidotes for me.