So many things! Just recovering my (device-bound, i.e. explicitly opted out of cross-device restores) 2FA authentication credentials, banking apps etc. takes me a few hours on iOS.

Restoring all app data and configuration would probably take me several days. The fact that Android still doesn't offer an equivalent to iTunes local backups of iOS devices was one of the reasons I switched.

I echo this. Having gone through several phones over the past few years, configuration settings just feel ephemeral, and there are headaches involved in porting them to different systems. And anything that's even remotely important gets backed up on a cloud.

At the least, contacts. Possibly local notes too.

If someone likes their layout, perhaps the config of their launcher.