Here is the full list of all 53 Persona 5 Royal achievements. It takes around 80-100 hours to unlock all of the achievements on Windows.
Watched the ending.
Completed every Palace.
Conquered the Reaper.
Evolved a party member's Persona.
Completed Mementos.
Ordered from the special menu at the maid café.
Attended the jazz club.
Completed the cruise ship Palace.
Completed the casino Palace.
Played a game of darts.
Visited a temple.
Passed time at the fishing pond.
Maxed out all social stats.
Scored the highest on your exams.
Completed the spaceport Palace.
Scored a prize in the crane game.
Customized a gun.
Completed the pyramid Palace.
Maxed out one of your Confidants.
Entered a special relationship.
Performed a Gallows execution.
Completed the bank Palace.
Performed an execution during a Fusion Alarm.
Performed a Showtime attack.
Couldn't take the heat in the bathhouse.
Played a game of billiards.
Sold old clothing at Furugi no Neuchi.
Completed the museum Palace.
Used Incense on a Persona in Lockdown.
Encountered a deviation in Mementos.
Traded in flowers while in Mementos.
Obtained a Treasure Demon.
Traded in stamps while in Mementos.
Obtained a Skill Accessory from a Palace ruler.
Performed a Group Guillotine execution.
Performed an Electric Chair execution.
Went to a hangout spot with someone.
Completed a Mementos request.
Established your own squad of thieves.
Completed the castle Palace.
Cleaned up in Leblanc.
Scored a hit at the batting cages.
Worked a part-time job.
Performed a Guillotine execution.
Defeated enemies via Disaster Shadow explosion.
Triggered a Technical.
Used the grappling hook.
Performed a Baton Pass.
Obtained a Persona through negotiation.
Obtained Arsène.
Unlocked all achievements.
Completely changed the cognition of Mementos.
Won the lottery.