I've been using Protonmail for EMail, and Etesync for CalDav and CardDav Calendar, Contacts and Tasks sync across platforms for the last four years or so with great success. I use the Etar app from F-Droid and Thunderbird on desktop with the Lightning and Cardbook add-ons to sync my calendar and contacts, though TB just recently added native support for CardDav I believe. I find both Protonmail and Etesync with the Bridge program and the Android apps is an incredibly easy, open source and encrypted way to keep your contacts and calendar access. The Protonmail Android app is a little to be left desired due to no push notifications or auto-updating APK now going on four years later for some reason.
If you are wedded to Outlook like some of us are with our jobs, you can use the DavMail bridge client to access the Exchange Server on desktop PCs with just about any email program you like, including Thunderbird. For Android access, you can set up a DavMail server (very complicated) to access your Exchange Server with K-9 Mail, FairEmail, and Davx5. On Outlook, you can access your Etesync calendar and contacts with the CalDav Synchronizer program. I have not gotten around to setting up the DavMajl server so I am using Nine Folders from the Play Store to access my work calendar emails and tasks, which uses Office365 sadly.