Here is the full list of all 20 Peeping Dorm Manager achievements. It takes around 5-6 hours to unlock all of the achievements on Windows.
Obtain all of Uehara Mirai's CGs
Obtain all CGs
Obtain all of Akizuki Misaki's CGs
Learn all skills from the gentleman club's instructor
While playing the plumbing mini-game, reach a full SSS combo
Fully dominate Miss Mango
Purchase all products from the supermarket clerk
Fully dominate Uehara Mirai
Collected all of Mirai Uehara's panties
Fully dominate Akizuki Misaki
Collected all of Misaki Akizuki's panties
Fully dominate Takanashi Otohime
Fully dominate Kinoshita Yuri
Successfully enter Mirai Uehara's room
Purchase all products from the gentleman club's manager
While playing the trash sorting mini-game, reach a full SSS combo
Get taken away by the police
While playing the cleaning mini-game, reach a full SSS combo
Successfully enter Misaki Akizuki's room
Successfully complete the tutorial.