The API is available since Android 4.4. The requirement to use it instead of asking for access to all documents, private photos, personal data and other data on the phone is there from Android 10 (that's 4 years now).
It's telling that the author isn't actually saying why they're rejecting him - I bet they're telling him the app doesn't need access all private photos just to sync a directory and that the app should use the API that's been mandated 4 years ago. There's even a fork that does exactly that and is published just fine.
Have you ever tried to publish apps on the play store? They often don't give you a reason that it fails, you're just left to keep trying different things randomly until it works, and then later fails again when you changed nothing... there is a documented history of this happening to many projects.
I know several FOSS projects that do not have the knowledge/time/desire to implement SAF support, and for some projects it doesn't make much sense or might be invasive to the user experience, and their play store versions have since been stuck at old versions and they just moved on to F-Droid and other appstores.
The policy there was always very clear - you need to use SAF unless you're building something that absolutely function with it (these are pretty much exclusively file explorers).
Syncthing can use SAF, the author just refuses to according to their bugs. This counts as "self-inflicted" and I'm not sure why they think they can complain their way out of it.
Many of those FOSS projects keep thinking Android is Linux, and then act surprised when it is not.
https://github.com/Catfriend1/syncthing-android#about-play-s...
Do you think Apple would accept that excuse?
Perhaps it only does this if the user wants to sync data outside the SAF?
I have switched to FDroid and download apps from there even if the same apps are available from Google Play Store. Like VLC, Syncthing, Ankidroid, etc.
I also switched to OSS alternatives from FDroid, deleting Play Store apps, and I have zero regrets. Some examples-
1. Antennapod is better podcast player than anything on Play Store, like Pocket Casts, Podbean, etc.
2. Voice is the best audiobook player for local files for Android.
3. Feeder is a great RSS reader. Can't use anything else here.
FDroid is not only useful, it is fun, too. I have an app called Bubble which is a spirit level app using the phone's sensors. It's like using Windows in the 00s, and discovering indie apps and playing with them.
It also has apps like Exodus where you can check permissions used by apps to check suspicious permissions.
