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