I used Nextcloud for both files and my PortableApps for years but it always had a hard time managing all those tens of thousands of small files. Lots of sync overhead. So I found Seafile and couldn't be happier. I don't just have my PortableApps in there now, I sync my Windows Documents, Pictures, Videos and Downloads folders. Seafile is very good at tracking partial changes in files so it doesn't always need to sync an entire file when just part of it changed.
Also: It's just a file sync service without any auxiliary features.
Yea ... no, sorry to say but this one's on Microsoft. I get it, hurr durr Apple expensive and elitist, but they know where to put up their walled garden and where not to. For example they used to have their own video container .mov but they're way past forcing something like that onto iPhone users. And even back then, the actual codec they committed themselves to in those days was H.264, a standard that's open to adoption by anybody. You can easily turn an old .mov into an .mp4 or .mkv without needing to alter the actual content of the file and that content is playable by pretty much every media device built in the last 15+ years.
HEIC isn't Apple's thing it's from the MPEGroup, also easily licensable by anybody. I guess the reason why it wasn't part of Windows 10 from the beginning is because they both came out in mid 2015. Windows 10 seems to have adopted it for viewing (and later editing) in 2018 but they make you hit a stupid download button in their store to get it so that's lame.