Real(near)time mutiuser checkboxes

One specific feature I’m using in Keep is near-time “checking off” (ticking boxes) items between users, or creating new items.

A ticked box would need to propagate to participating users in less than a five seconds. Web and Android are the target platforms. I can install any client and any server (FLOSS of course) but ideally I’d like to graft onto a Nextcloud install (which can be adapted in any way too). The number of connected clients is less than 10.

(I guess this is technically a line-by-line multiway sync?)

Is there a way to do this with Nextcloud + notes, or Joplin + Nextcloud, or Joplin + Joplin server, or …?

Thanks in advance…