Android

Google Wallet (or whatever they call it these days) doesn't work, even if you install Google Play Services. So NFC payments are simply not possible for me. I've heard that some banks have NFC payments built into their apps, but I have never seen a list. I'd switch banks if it meant I could get this to work.

There's currently no NLP (network location provider) support, so if you don't have an actual GPS satellite signal, you will not have active location unless you use Google's location services. There's been some talk of including a new NLP service in the future but I don't know of any timeline.

Even when using Google Location Services, accuracy is worse than on the stock Pixel OS. I'm not sure why, but I get tons of drift indoors (whether Wi-Fi is enabled or not), whereas on PixelOS it was almost always stable. It also means navigation apps will sometimes think I magically hopped off a bridge and onto the side street below or something like that.

There's no "extreme battery saver" mode like on Google's Pixel OS. When I switched, I didn't realize that was a Google feature rather than an Android/AOSP feature.

If you rely on Google backups for app data, I'm not sure if there's any reasonable way to get that into GOS since it can only happen during initial setup. Might be solutions to this, but personally I didn't spend time on it because there was nothing I cared too much about. Check your apps to see if they have settings import/export functions. A lot of open-source apps (like Lemmy clients) do.

GOS has an open-source backup system called Seedvault, but of course if you ever want to switch back to a stock Android OS, you won't be able to bring those backups with you since apps simply can't get that level of access on any stock Android OS. You're stuck on GOS or other third-party OSes that support Seedvault, or maybe rooting if that's possible.

If you use WhatsApp (ew), be aware that it only supports backup via Google Drive. And you can't manually download and restore that backup without adding Google Play Services and logging in.

Lawnchair and other third-party home screens seem to work worse on GOS than stock Pixel OS when it comes to the app switcher animation bug. I've seen some GOS forum threads about this so I know I'm not alone.