I have replaced a tile floor that ran under cabinets without removing cabinets. we chipped out the floor up to cabinets. Then laid new tile and added shoe molding. If you are going to change your layout later, buy extra tile because it will be discontinued, and you will not be able to find it later.

You can replace just the floor. There are several cautions.

Do not increase the height of the floor in front of dishwasher/other under cabinet appliance. That will prevent removing that unit if necessary. Or removing the countertop.

You will need to cut the old flooring as close to the cabinet bases as possible. That becomes a huge water leak situation as well as a dirt catcher and eyesore. You will need to seal the gap and install some kind of trim to minimize dirt/water/look problems.

If there is damaged sub flooring that extends under the cabinets, that is a fairly serious situation. Patching should be done by replacing the entire area---even under the cabinets.

When the cabinets are replaced, matching the flooring height will be the major concern. Unless the new cabinet footprints are shorter---and expose more of the old flooring.

I replaced just the floors in a condo. As others have posted the issue Is the height since you don't want to trap the dishwasher.

In my case, I was replacing with some kind of vinyl tile so height wasn't an issue since the vinyl tile was relatively thin and it was just placed over the concrete sub floors.

In my current remodel, the new wood floors are significantly higher than the old floors so it would have been quite difficult to run such high floors in the kitchen. Even if I took out the dishwasher to install new floors under the dishwasher which is relatively easy to do, I suspect the dishwasher would then have been too tall to fit under the existing counter.

A NEW build rarely has flooring under perimeter cabinetry. Cabinets are SHIMMED to accommodate the floor install., which is usually installed near the end of construction for obvious reasons. Pull the dishwasher out, remove any tile or whatever first. At this point, a pull of the toe kick and replacement of same/with shoe mold if necessary at all perimeters after new is installed.

I don't know about rarely but I definitely have "flooring" under the cabinets. All of the under layers were installed and there is a layer of plywood equivalent in height to the hardwood top layer that is installed under all the lower cabinets in the kitchen. The tile floors were installed under where the vanity cabinets will be installed.