When you're in the Minotaur's area, at the part where the paths branch, you go right until you find the Minotaur's room. Inside should be Alexandra, and you should need to either interact with her through the bars of her cell or talk to the minotaur. If neither of those work let me know, i might need to take a look at your save file to see if something's gone wrong.
I don't think you can directly add files to itch comments, so the easiest way would be to use some free file sharing site, like this one. https://filebin.net/
Just zip your save folder and upload it to there and I can download and use it. (I need the global.rpgsave file from your save folder as well as whatever save file you'd like me to load.)
Okay, based on your save it looks like you lost to the Minotaur and completed the entire defeat route for that, which should have sent you out of the dungeon. Did you maybe finish that and then quit playing for a while, then returned to the fourth dungeon without realizing you'd finished it? Or maybe the event bugged out and didn't send you out of the dungeon after the final defeat scene. Either way, on top of that, the event to exit the dungeon was supposed to be set up to let you leave if you showed up there after the defeat route, but it wasn't set up properly. I'll fix that, but for now you should just use the "Debugger" key item in the menu, select "Teleport to Elmgar" and then go to the guild and talk to the purple-haired receptionist to start the fifth dungeon quest. Thanks for the bug report.
Well, i have a problem that purple-haired receptionist is missing