What I dislike about Zotero is that it's a pain in the ass to self host. In my department I could spin up a local Zotero server for our PhD students and give them basically unlimited sync, but it's really finnicky
What difficulties are you having? All you need is WebDAV. I use a nextcloud server for mine and my partner's zotero storage, and its entirely trivial to set up.
I have many issues with Zotero (which has been dumbing down at the expense of power users for some time) – but easy private sync is definitely not one of them.
Looking at my own Zotero account, I can confirm that all metadata storage is free and not counted (I am using none of my 300Mb storage in my account according to zotero.org, despite syncing metadata for several thousand bibliography items). The only storage Zotero seems to count is attachment storage, and that's all synced via my WebDAV.
I thought the discussion was about self-hosting data, such that the provided free storage limits by Zotero remained sufficient? And for that use case, self-hosted WebDAV storage for file attachments is absolutely fine.
(The poster I was replying to was suggesting that their departmental users would go over their storage limits for metadata alone, even if they used WebDAV for attachments -- but that seems to be incorrect from my own experience, and everything I can find online.)
It is not supported natively (you can use a webdav server but it doesn't sync everything) and the third party options don't have the level of stability I'd need
