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

It’s technically possible, but windows doesn’t give you as the user tools to do so. If you donÄt want windos to have the ability to do so you could use full system encryption like: https://wiki.archlinux.org/title/Dm-crypt/Encrypting_an_entire_system