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