The most critical apps for me on mobile are banking, payments, transportation, and messaging. Banking I can’t do much about. Payments I can still handle with physical cards. Messaging is getting better thanks to people adapting proprietary services to Matrix, so with some effort you can use one open source client to reach them all.
Transportation is the area I’ve been working on. I’ve been getting MapLibre (an open source map rendering library) running on Compose Multiplatform, including Compose Desktop (so map apps built in Jetpack Compose could extend to Linux based phones like Librem) and also on Huawei’s HarmonyOS. If I can cover my everyday needs with open tools, then walking away from the Google/Apple duopoly stops being a thought experiment and starts being a real option for me.