So, here they are:
Palkia(though it can be obtained through the Ultra Unlock: Space happening from August 6th to the 20th, which is unlocked through completion of tasks during GO Fest)
Dialga(though it's available in the Time Unlock)
All other Legendaries can be shiny
Also, pretty sure you know this, but Go Fest '21 already ended.
Source: Serebii Pages on both days of the GO Fest