It’s hard to see what this is but if it’s just ducting, they sell end caps for radial ducts at big box stores. You would stick that on the end and wrap it with some aluminum HVAC tape. But it’s not really hurting anything as it is. Probably just vents outside.
How to seal this open duct? ( lemmy.world )
Found this in a cabinet under the stove. I think it’s old ventilation from before the induction burner was installed. Not sure how to seal it off.