Not sure how common this bug is, couldn't find any info about this so I'm leaving here in case someone needs it.
So the symptom is that the rendering time goes abnormally long. I mean, really too long. What should be 10min render turns out to be 100hr when the export button is pushed.
The cause of the issue is that there's a video clip that tries to render along with original still view that you intend to render. Mind you, no video is selected in the export window yet it renders it without telling you. The camera setting is from that video clip yet it takes the render setting of the selected still view. (which makes the expected time scale with intended still render quality)
I could identify the culprit by letting it render for while with very low setting and when I cancel the render process, there was unexpected video file that was half finished.
Fixing was simply to get rid of the video clip in the media window of the twinmotion. Now the still image renders with normal time frame.