Persona 5 Royal removed the most game-breaking exploit from the original Persona 5 as part of the wave of combat and difficulty balancing improvements.
It's over, everyone. The most meme-worthy exploit from Persona 5 no longer works in Royal: you can't destroy all semblance of level progression by waiting for the Reaper to die from a bad case of the sniffles during flu season. Abusing the poor Mementos targets for money has been nerfed as well, with the Confuse status effect only lasting one turn and making the whole exploit much less efficient.
Both of those strategies are time-honored for Persona 5 veterans, and some might be sad to see them go, but the various improvements made to Mementos alongside other overhauls like fusion alarms, technical ranks, and the much-improved baton pass do a lot to soften the blow. Fans turned to the exploits because Mementos could often feel like a brutal slog; spending hours trying to gain levels the way the game 'wanted' players to was an exercise in masochism, so abusing minibosses and the Reaper for cash and experience became much more tempting.
So how do the mechanical changes to Royal replace these beloved exploits? For starters, players can utilize Jose, a strange little boy with a penchant for flowers, to make grinding in Mementos much more efficient. In exchange for the collectible stamps he's placed on each floor, Jose will offer to change the cognition in Mementos and increase the rate at which players gain money, experience, or items during their exploration. Since the buffs to EXP and cash can go up to 200%, they add up fast.
To make things even smoother, Royal also fixed up Ryuji's rank seven confidant ability, Insta-Kill. The ability provides the full amount of experience or cash a battle would have otherwise given, so it means you can simply vehicular manslaughter your way through easy battles and skip the grinding.
As for the Reaper, as fun as harassing him may have been, he wasn't supposed to be that easy. Beating him down in the early game allowed players to more or less trivialize the rest of the content because of the massive experience gains and the Divine Pillars he dropped. It may seem like Atlus took away the players' favorite toy, but NG+ exists for those who want to curb stomp their foes into fine dust from the first palace onward.
The difficulty balancing has impacted his fight for the better as well - while it's still hard, players who are quick on the draw can make good use of the new Persona traits, improved technical damage, and buffed baton passes to bring the Reaper down a notch or three.
To sum it up: even though Royal doesn't let players break the game quite as easily as they once did, the streamlining of Mementos grinding combined with improved combat means there's not as much need to break it. The game feels more balanced in Royal, so players on most difficulties shouldn't find themselves hurting for cash or levels if they drop into Mementos now and then to catch up on requests.