I'm using Google Drive, mounting it automatically after logged in in online account, but I've read that Google Drive mounted doesn't keep a offline copy of the drive so any access take a long time. Is there a way to force Google Drive to be cache offline?
The simplest way (imo) for 20.04 is to use google-drive-ocamlfuse. I don't know whether it is compatible with 18.04 or 20.1 but it's the best way for 20.04.
Because of a change of security policy from Google, Nextcloud 13 and ownCloud have removed support for Google Drive external storage, but accessing Google Docs files offline is supported by the Google Docs Offline Chrome extension offered by google.com. After installing the Google Docs Offline Chrome extension return to Google Drive and navigate to gear icon -> Settings -> Offline, and enable Create, open and edit your recent Google Docs, Sheets and Slides files while offline.
Access Google Docs files offline
To turn on offline access:
Source: Use Google Drive files offline – Google Drive Help
You may use https://www.insynchq.com/downloads It has 15 days trials and then 30$ one time, if you are ok with not syncing team drives.
From free apps - there is https://github.com/gdrive-org/gdrive
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Comprehensive answer here: Is there a Google Drive client available?