I would suggest a baikal server: https://sabre.io/baikal/docker-install/ it’s made from.the ones making radicle and sabre, one of the kost used open source caldav/carddav servers. Yes it can sync calendars too

the problem i see with nostr is that it implements a bunch of pro-cryptocurrency ideas: like paying to use relays for example and with all the sustainability issues regarding crypto and us wanting to create a better network, i would like to leave money out of it

But it’s definitely possible to ship a virus embedded in a playable mkv file, but something else would have to extract it first, for it to do anything

if you really only played it and it didn’t abuse some zero day in vlc (extremely unlikely), the there’s basically zero chance you could have activated a virus.