The Ki-Fueled Attack optional class feature for monks states (TCoE, p. 48):
If you spend 1 ki point or more as part of your action on your turn, you can make one attack with an unarmed strike or a monk weapon as a bonus action before the end of the turn.
But looking over the monk abilities that cost ki points, it isn't clear to me exactly which ones count.
Clearly even though bonus actions count as actions, those won't work because you're limited to one a round. Reactions are rarely on your, and some abilities that cost ki points are spells (e.g. the Four elements monk) so you would need to check each one (having looked they all seem to be actions).
This does leave some strange situations where more offensive abilities (like Aspect of the Wyrm) are not compensated whereas, say, casting Pass Without Trace as a Shadow Monk does let you make a bonus action attack.
As an action, you can spend 2 ki points to cast darkness, darkvision, pass without trace, or silence
Further complications are where you can take a regular actions, and either spend ki point on the condition of causing damage or otherwise, e.g. Deft Strike:
Deft Strike. When you hit a target with a kensei weapon, you can spend 1 ki point to cause the weapon to deal extra damage to the target equal to your Martial Arts die.
Because I'm almost certain there will be monk abilities that I think count that don't and vice versa, as well as the fact I'm trying to pick a subclass for a character I was hoping to find out which of the many monk abilities count for this optional rule?