“All Dynastic Actions must be either Mandatory or Optional.” means that anything defined as an action by the dynastic ruleset is Mandatory. (They must be one or the other, and the appendix clarifies that when something is undefined it takes the alphabetically earliest possibility.)

This currently includes Generating Time, resolving tied Timers, and the “When it is an Island’s Turn, they must carry out the following atomic action…” - meaning that step #1 of that atomic action will always include performing another instance of that atomic action, and that a player taking the action can never complete it. We are still waiting for Tantusar to finish their opening turn, which cannot be finished.