RMN is short for RetailMeNot. RMN has a website and an app, and deals/opportunities can vary slightly between them.
Target GC to GC is dead. Same at
Best Buy. The only place currently consistently (although there were a few sporadic reported exceptions) offering GC to GC is
Walmart/Sam's Club. Target Red Card will still get you 5% off gift cards, but with a decent rewards credit card, you can do a little better at Sam's or BJ's without extra effort.
People have mostly had good success with an app called DOSH that tracks your CC purchases and offers cash back. Sam's Club is one of the companies that offer cash back. Currently it's at 2%, but sometimes jumps to 8% or even 10% for short periods. This is (currently) stackable with a similar program through Uber Local, where you can earn 5% Uber credit for purchases made at Sam's Club. Filler item is required, and results are quite a bit more YMMV, with most people having reported getting credit on some trips, but not all.
Another higher-yield method is to purchase GCs at Best Buy (not using GCs to purchase), but using Swagbucks in-store rewards program to earn 9.5% back in Swagbucks. You can also earn Best Buy rewards through these purchases for another 1-2% back, but those rewards are no longer redeemable for gift cards.