Have you heard of [syncthing](https://syncthing.net/) ? It syncs a folder between devices, like Dropbox, without the need for someone else's computer. No cloud, it's just your pc talking to your phone, directly and automatically, through your home WiFi.
I’ve found LocalSend really nice for this purpose. If you need to send stuff over your wifi to other devices but not sync it in the background it’s really nice