hi!

looking for some good recommendations for action... preferably with a weak to strong character/one that hides their strength or power/mc has amnesia or something...

thank you!

In Kimetsu no Yaiba, the mc starts off weak and gets stronger gradually.
Also, one of the other primary characters thinks himself weak and often gets scared, even though he's actually quite strong.

The Breaker also has an mc that starts off weak and gets strong later on. If you end up liking this one, give Veritas a read too, since they are very similar.

In Boku no Hero Academia "weak to strong" is the central theme of the manga

Lastly, in The Eminence in Shadow the mc is really strong from the start, but actively hides his power. Don't know if it will have enough action for you, but it is hilarious and it is definitely worth a read

Be careful of your thoughts, for they will become words.

Be careful of your words, for they will become actions.

Be careful of your actions, for they will become habits.

Be careful of your habits, for they will become character.

Be careful of your character, for it will become your destiny.