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.
Not much to gain except more privacy and fully open source. A downside is there are less extensions available since it gets extensions from Open VSX Registry. Also there are extensions out there that are not good for privacy.
I still think VSCodium is worth it however.
Using goolag play services will always decreace your privacy.