you have to double click or double hit a key to advance every single bit of dialogue, idk why its like that by default. but in settings select "auto-delay" bar to highest to change it so just press a key or clicking once will advancing dialogue like normal.
can't save during dialogue choices, the UI at the bottom vanishes during them. same for when selecting "hide" as there isn't any way to make the UI reappear back afterwards, not even pressing "H" like most visual novel games would.
The click is working as expected in the cases you pointed out. Regarding not being able to save during the dialogue choices, we defined that to force people to replay the game and find the content in the way we expected. Lastly, we'll implement the H hotkey to show the UI as other novels do (thank you for your suggestion). For now, if you click using the right button of the mouse, it will be visible again.