Nextcloud is selfhosted, yes. But managed solutions exists, so you dont have to set it up your self/maintain it. (Free instances seem to exist https://nextcloud.com/sign-up/ dont know about privacy/encryption on these tho)
I am using Nextcloud Calender + DavX5 (android) + etar (android) for my colaborative and synchronized calenders. Working good since 1 year.
Nextcloud is selfhosted, yes. But managed solutions exists, so you dont have to set it up your self/maintain it. (Free instances seem to exist https://nextcloud.com/sign-up/ dont know about privacy/encryption on these tho)