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