How to sync/connect Nextcloud calendar with Google calendar continuously?

[j-ed]

I think searching for “vdirsyncer” will provide the requested information, like e.g.:

Vdirsyncer for sync calendar

Accessing an ics file is only a subscription, but not a real two-way-synchronization. So using vdirsyncer might be the better decision. As usual you find information about a program on its official website: http://vdirsyncer.pimutils.org/en/stable/config.html