I’m already, running selfhosted ResilioSync…
It’s completely 100% p2p (it uses bit torrent protocol - the first iteration of the product was called “btsync”) - but I have one machine I consider “the master” or “source of truth” - that’s ResilioSync (RSL) running in a FreeBSD jail on my FreeNAS NAS. I punched a dirty great hole in my firewall (exaggerating a tad 
) to let a certain port get forwarded to the receiving port that RSL peers listen on - which goes to my FreeBSD jail. I have clients running on :
- MacOS - Macbook Pro M1 - MacOS 11.4/5 or whatever
- Linux - Ubuntu 21.04 running on x86_64
- Linux - Ubuntu 20.04 running on x86_64
- Linux - Ubuntu 21.04 running on arm64 x 1 (RPi4B)
- Linux - Raspbian Buster on arm64 x 1 (RPi4B) - my pi-hole, OpenVPN and SSH jumphost
- Linux - Raspbian Stretch on armhf x 1 (RPi3b) - my TVHeadend server
- Linux - Raspbian Buster on armhf x 1 (RPi ZeroW)
- Windows 10 - Dell laptop on my desk at work
- iPad Pro 12.9 iPadOS 14.x
- Galaxy S9+ phone Android 10
- Linux - Armbian / Ubuntu 16.04 on arm / sunxi : BananaPi - my transmission-daemon server
- FreeBSD : i.e. the master in a jail, but I also have portable version I run as my user off my home drive of the NAS to sync my bash shell scripts
What I need is something “in tandem” to these - that makes it relatively easy to collaborate and share stuff with family, friends and colleagues. RSL aint that easy - sure I can send a link for something and they can maybe get the file - dunno - but - would my MUM know what to do? Could my brother show her what to do?
I can email a RSL link to a new share to anyone I care to - but - when they get the link and try to open it - how will it know to reach from externally, into my internal network, and, it only works if the receiver has the client application installed anyway, even if they were on my LAN. I’d only share this way to other computer geeks, and probably only Linux / UNIX computer geeks…
and @Akito - took a quick look - icecloud looks okay - but - there’s no snap for arm64 (not that there’s an arm64 app for Dropbox either)… Your webdav solution looks interesting… Might be tempted… but right now - Dropbox is too easy - ideally what I’d like from Dropbox is half the storage, for half the price… Note : most solutions for using Dropbox on RPi seem to be using webdav… Years ago - I used to use unison to push/pull sync data, but it was cumbersome…