I agree. I used it for 10 years on reddit (I paid $0.99) and bought the lifetime ad removal for the Lemmy version when it came out. It's not what OP is looking for though.
If Sync didn't exist I would use Thunder. It works well, has a nice interface, and is FOSS.
I just dropped Sync. I've used it for reddit since the app came out. Even paid for the premium version years ago. My purchase didn't carry over to the lemmy version, and I noticed the app collects data for marketing now. Switched to Voyager, it's not as fluid as Sync but I'll get used to it.
Jerboa and Eternity are native Android apps (the first uses modern technologies like Kotlin and Jetpack Compose, the second one has a lot of Java code and the UI is made with XML layouts for activities/fragments);
Voyager is portable web app built with React in Typescript, with mobile flavours made using Ionic capacitor;
Thunder is a cross-platform app built with Flutter in Dart (like Liftoff and Lemmur were in their days);
there are other FOSS apps like Combustibile (native/Java+XML) or Muffed (Flutter)...