That's just a return and there shouldn't be one in the kitchen by code where I live, so I would just cover it up. Returns don't belong by kitchens or in bathrooms for what should be obvious reasons.

I would simply block it off and add a return somewhere else. Depending what's on the other side of the wall, you may be able to simply mount a wall vent on the other side and cut a correct size hole and eb done. I also would not reuse that vent as the vents in the baseboard trim are an unnecessary pain. Truthfully most houses have more return than they need, so you may not even need to add one, but you would need to do some math before simply just blocking it off and walking away.

HVAC guy for almost 30 years.

I would not do anything with my cabinets to accommodate this vent.