Weird black line/artifact in photo? (XT4 + Canon FD)

So since I last posted a few months ago, the problem has cropped up again. Just to summarize:

1. Camera was purchased in Summer 2021.
2. The problem first presented December 2021.
3. I took the camera back to the store in February 2022.
4. They sent it to Fujifilm Netherlands. 2 weeks later it came back saying they found nothing, but they updated the firmware and "adjusted" the sensor.
5. I picked up the camera and tested it for one day, with new SD cards. Same problem presented again.
6. I gave it back, and they sent it to Fujifilm Netherlands again, who sent it to Fujifilm UK.
7. About 2 months later they sent it back to me, without letting me know what they did. They said "we found the problem and fixed it".
8. So a week after I received it I tested it out again, and the problem presented again. The problem presents with different lenses and different SD cards. So it is definitly a problem with the camera.

I have now sent it back to the store again and said I expect them to replace the camera. They are making a big fuss that they normally should get 3 attempts to repair. I disagreed.

They then said they will send it to Fujifilm again, they will take a look, but will not try to repair it again. Just confirm something is wrong, and then I will get a new one. It has something to do with Fujifilm crediting them for the camera or something. In the meantime they would send me a loan camera (XT3), which they did. Over a month has passed and I have not heard a peep out of them regarding the XT4.

So will send them another email asking whats up. I really hope I get a new XT4 back for my vacation middle of August...

If anybody has tips on how to deal with it let me know.