The only thing I read about that, and again I may be missing something, is:

"UAA and SUI also commented that pilots who obtain an unrestricted ATP
certificate with 1,500 hours would need a minimum of 2,500 total flight hours to upgrade to a
part 121 PIC. SICs with an R-ATP certificate would need a minimum of 1,750 (military pilots)
to 2,000 total flight hours (graduates of qualifying four-year aviation degree programs) to
upgrade to a part 121 PIC."

https://www.faa.gov/regulations_poli.../2120-AJ67.pdf