Hi there! Thank you so much for playing!
Yes, there is a true ending. To get it you must go to the Brandon's bedroom after getting the strange pendrive and before entering the Command Bridge. It is the first room after the Deck. Go inside and interact with the computer-thing at the corner, then you'll be locked at the true ending. (For some reason, Itch isn't allowing me to post the screenshot here, so use the link to open the image)
https://drive.google.com/file/d/1b_3p8eO7ao-0bCH0XdnTuTuN45R2H_U7/view?usp=shari...
To travel the gas you must find an Item called "Gas Mask", it's on the second floor. Finding it and entering that room in the greenhouse let you start a side-quest and explore 3 additional dungeons with exclusive enemies and fight "3" new bosses. You'll be able to unlock that locked door after completing this quest.
And the "Irina: Maid Costume" is indeed bugged. I'm fixing it and will update