offline site version

I want to make a cultural event management website with an offline version synchronized with the online version.
Authenticated users of the site must be able to use it even without an internet connection from their mobilephone (possibility to install a mini web server on the phone).
Changes made during the offline period must be synchronized with the base of the main site when an internet connection is available (synchronization in both directions according to rules established in advance).
I am on drupal 8.
Could you advise me on modules or techniques to do this?

Drupal version: