So I know about the different requirements for an ATP vs R-ATP but I can’t find what you are able to do with a full ATP that you can’t do with an R-ATP
All of the limitations of an R-ATP can be found in 14 CFR 61.167, Airline transport pilot privileges and limitations:
(b) Limitations. A person who holds an airline transport pilot certificate and has not satisfied the age requirement of § 61.153(a)(1) and the aeronautical experience requirements of § 61.159 may not:
(1) Act as pilot in command in operations conducted under part 121, § 91.1053(a)(2)(i), or § 135.243(a)(1) of this chapter, or
(2) Serve as second in command in flag or supplemental operations in part 121 of this chapter requiring three or more pilots.