Google has such rampant influence that it’s difficult to block them completely with uBlock Origin or DNS solutions. However their corrupt surveillance can be reduced using some of the tactics and software in this article: https://simplifiedprivacy.com/how-to-reduce-googles-control-over-you/
Filen wasn’t very good. I tried it and their client was annoying. It refused to run in the background like a proper service and the GUI would pop up on every boot.
Filen is also just a file sync and backup service, not comparible to Nextcloud which has many more features.
I want to try Nextcloud next but I suspect it doesn’t have a background service for backups and syncing?
For calendar and contacts I use EteSync since it uses E2EE just like Filen. Nextcloud is good but it does not have E2EE as a supported feature. There is a broken E2EE plugin for Nextcloud but only for files.
The Filen client works fine for me on Linux. It runs in the background and does not pop up after boot.