I didn’t test for N-antibodies so I don’t know.
No idea what “ruin” means, is there any scientific support for that or just antivax FUD?
There actually was a study in the Netherlands that seemed to imply something like that about the boosters. Not vouching for it as I have no info about their bias or lack thereof.
Israel seemed to stop the rollout of the 4th booster for reasons that seemed to imply this as well, but again, I don't have much clarity on that.
ETA: It was a Danish study.
Here it is. Make of it as you wish.