Email, Jitsi, Matrix/Element, many of them, e2e encrypted and on-premise. No serious company (outside of US) which really care about it's own data privacy would

Email, Jitsi, Matrix/Element, many of them, e2e encrypted and on-premise. No serious company (outside of US) which really care about it's own data privacy would go for MS Teams, which can't even offer decent user experience most of the time.