Do any of the options you listed work reliably?
Litmus test: sync a few million files totaling a few terabytes, including build output directories. Build a few projects on machine A a few times and run the unit tests (most services desync at this point). Perform a full sync of A and then machine B. Build on B. Repeat. Also, on both machines add non-overlapping files (like pictures, screenshots) to the same directory at the same time.
You're looking for storage. Not sync. the clue was "terabytes". Wanna know where i draw the line? you can't sync terabytes to a phone.
I'm not trying to sound like a jerk. All of the things we mentioned are software based airquote "storage", dropbox, syncthing, etc. your original thing was "shared a folder with SO" which is why i asked what the folder was, mostly. Matrix will gag encrypting a TB of data. Misskey's drive defaults to like a gig per user.
Get a NAS, tailscale (or whatever, set up your own VPN with a fortigate or something), and now you rely on no-one but your ISP(s).
Proof that this works, just fine: https://imgur.com/a/q9hLDeH
note: I use both nextcloud (with a real domain name and certs and everything!) which is a VM on one of our machines in a DC. the synology is at my house. The synology backs up to a dedicated machine (it's in an air conditioned outbuilding with dedicated fiber pulls) with it's own redundant storage array, but that machine is "asleep" 99.9% of the time unless i'm pushing backups. My synology is not publicly accessible. It has ~30TB of storage, iirc.
note2: that youtube-rips is 90% <=480p, too!
As for besides NextCloud, just to check my blind spot.
and look, i am sure qnap and Aghyzzicgh from aliexpress might do this too, but i can't speak to them. I bought a synology on recommendation from a friend. My first one got hit by lightning (yes) and i had to buy a new NAS but the drives still work. i've replaced the original drives, but they still work. i installed one in my kid's machine to hold games. My current synology is a 4-bay dualcore with 2GB of ram.
it works perfectly for all this stuff. my phone automatically backs up photos to it when i connect to wifi, for example. If you put your syno on a public IP, you can hotlink to content on it. there may be ACL shenanigans, i have no idea. I don't use it that way.
why don't i use my synology that way?
Because i run a public nextcloud instance to be able to synchronize my photos and documents and hotlink them.
derp https://nextcloud.projectftm.com/index.php/s/synoscreenshot
I love Immich [0] for photos, Jellyfin [1] works great for music and movies, just spun up a memos container for notes. For documents and stuff I would use dropbox for I just FTP into with Cyberduck or Filezilla.
But what do you actually need to share? Folders? Or links to content? PDF? Archives?
Matrix homeservers and clients support most mime types in chat, including zip, so you can send anything and have it searchable in the chat as long as you maintain the matrix server.
Misskey has a "drive" feature, where all media you share goes, but you can also upload directly to it and link directly to media in the misskey drive.
Pastebins work, too. My github^ has the instructions on how to set up the same thing I run, an Up1 pastebin. I'm sure there's better.
But nextcloud has first class mobile clients, understands folders and mime types, can be synced over WebDAV, cifs, http, etc.
So... Up to you?
^ https://raw.githubusercontent.com/genewitch/opensource/refs/...