Modal Triggered Ability Timing

[Reeplcheep]

When a triggered ability without a target is placed on the stack, do you have to announce modes or only once it has resolved?

Some examples:

Felidar Retreat
Black Market Connections


I know modal spells you need to announce when you cast it, such as Gruul Charm

[H]

when a triggered ability without a target is placed on the stack, do you have to announce modes or only once it has resolved?

603.3c if a triggered ability is modal, its controller announces the mode choice when putting the ability on the stack. If one of the modes would be illegal (due to an inability to choose legal targets, for example), that mode can't be chosen. If no mode is chosen, the ability is removed from the stack. (see rule 700.2.)