The LORs that are an official part of your application are to be submitted using a form that asks questions that need to be answered by your recommender. Like who they are, their relationship to you, contact info and whether the recommendation is confidential.
Loose LORs are not officially part of your application except for in rare situations.
These days, many high school kids do research, are mentioned in publications, have internships —“many” meaning those in the working towards highly selective college acceptance crowd. Too many for that stuff to have much merit anymore. At one time, it was rare, and therefore packed more of an impact. Reading through this forum, one comes across hundreds, more, of high schoolers doing research.
Yes, such a LOR would pack a punch if that Professor was well regarded at a college and he personally went to bat for you. Wrote a letter AND made a personal trip to Admissions and said, “I want this amazing kid here”. Admissions gets all kinds of letters from alums , professors, celebrities saying how great kids are. Like thousands of them. Unless it gets to AO through a very personal channel, with heavy weight, it means nothing. An AO doesn’t have the Tomé to assess the research , the prof and determine whether it’s not just one of those standard good Will LORs. Gotta do a lot more to make a difference.