I recently came across a sentence with 深深感动 in it. Can 深深 be an adverb without 地？ For example: 让顾客和所有参与者都深深感动
You can use 深深 as an adverb without 地
From my answer to this question
Adverb with 地 emphasizes the 'manner of the action'. For example '大力地打'
Adverb without 地 focuses on the verb itself, with the adverb as an equal-weighted complement. For example '大力打'
A single character adverb doesn't usually use 地. For example '痛打'，'狠批' (never '痛地打'，'狠地批')
figure out the difference between 的，地，得（all are pronounce de but with different tone)
they are fixed expressions.
chinese adj + 的 + noun.
adj + 地 + verb.
adj + 得 + degree verb.
so in this case, 深深的 is an adjective, 深深地 is an adverb. 打 means to hit which is a verb, so 用力地打 is to hit hard. and you can say 用力打 without 地 for it is a fixed expression.
for those words/phrases can either be a verb or an adjective, you could still speak without 的/地 in most cases ‘cause we can figure out whether it is an adv + verb phrase or an adj + noun phrase according to the context.
take 打击, which means blow, for example
此次行动 对 敌人 造成了 沉重(的)打击。=> this action has made a great blow on the enemies.
此次行动 沉重(地)打击了 敌人。=> this action greatly hit the enemies.