Vishnu is in Adityas (sons of Aditi) too.
Bhagavad Gita 10.21
आदित्यानामहं विष्णुर्ज्योतिषां रविरंशुमान्।
मरीचिर्मरुतामस्मि नक्षत्राणामहं शशी।।10.21।।
Of the sons of Aditi, I am Vishnu; of the luminaries, the radiant Sun; of the Maruts, I am Marici; of the stars, I am the Moon.
Vamana (an incarnation of Lord Vishnu) is Aditya (son of Aditi) or Upendra (younger brother of Indra). Vishnu is mentioned in Adityas in this question's answer too.
In Rigveda, as more preference is given to 33 koti (type) Devas (12 Adityas, 8 Vasus, 11 Rudras, 2 Ashvins (or Prajapati and Indra in another list) and their family) and not to the Trinity directly (I mean preference is given via a post named Prajapati (to Bhrahma) and Rudra (an incarnation of Lord Shiva)).
So, are there some richas of Rigveda dedicated to Vishnu who is from Adityas and not from Trinity?
English translation of Rigveda 1.22.18 might be talking about Vamana (from Adityas) but not sure. Are there any other richas, as one member of this user has asked this and this question which means there must be some richas which are dedicated to Vishnu from Adityas or Vishnu from Adityas is mentioned in richas which are dedicated to Indra.
What will be the interpretation of Bhagavad Gita 10.21, is this Vishnu from Trinity or Vishnu's incarnation as a son of Aditi?