I'm a long time ownCloud/NextCloud user and I'm aware of the alternatives. With multiple android phones come and go in the past 8 years or so, the background upload seems to stand its ground.
The real problem here is iOS and its lack of proper background tasks. See: https://github.com/nextcloud/ios/issues/215 -- they tried every possible way to persuade iOS into running background sync, but still hit and miss.
I have to request access to my wife's iPhone and manually trigger some :)
One small suggestion here -- PhotoPrism went with `tensorflow.js` to load up classification models, and I recommend a "real" TF or PyTorch installation to properly leverage the computation resources. The difference is huge even running cpu-only because it's wasm vs. proper BLAS library.
I worked on a nodejs binding for native ONNX runtime (not publicly) so that's also a possible way out.