While millworkman is technically correct, I doubt the thickness of an LVP floor plank would dangerously alter the gait of a stair. You're allowed a 3/8" deviation between treads over a run.

Somewhere I saw where a guy had thermoformed the front edge of his LVP planks to avoid the expense of purchasing the factory stair treads. It looked fine, however, he did not have the compound bend on the end of the tread as shown in the picture. That's problematic.

The assembly is white. Leave it white. The assembly may look better without a need for the newel post quarter round. And with a bit more caulk.

I would be replacing all of the steps with lvp. The bottom step is the problem and I have had one installer say that versatrim could make a tread to match my lvp that would be very thin and wrap on the bottom nose. But it would have an exposed edge on the bullnose. They could put trim up to to where it wraps.
I was thinking maybe extending the sides with some wood boxd so that the versatrim piece would be a little less noticeable.

Just make sure your stairs remain to code. As soon as you change the SURFACE material (you currently have carpet) to something new, you need to ensure the stairs are still to code. The installers might not be able to tell you if they will maintain code or not. A finishing carpenter is the guy you pay to work with stairs.

CoreTec is not a thin product. The planks can be quite thick. I cannot find the thickness of this product in the link. I'm going to guess it will alter the rise-height of the treads. That can be an issue at the bottom and the TOP of the stairs (what's up there? is it more carpet). That's more of an issue to me than how to finish a rounded presentation such as your bottom stair.

And once you alter the surface of the stair with a different material than is currently there (currently carpet) you *might have to bring the entire stair case to current code (no more grandfathering). It may not be the case. Your local building codes will tell you what needs to be done to stairs when you resurface. A finishing carpenter can be found and paid (they are the most expensive guys who swing hammers in the building industry) to deal with the code issues.

I would be concerned if your installers do not know the 15+ codes for stairs (most don't...cause that is many more years of education than they have).

Please check your requirements for those stairs.

Thank you. Valid point!

I am having the same issue. Kathy - what did you end up doing? floor guy said he could just cut the round edge and make it square

I wound up getting rid of the extra quarter round and went to the post and then filled the edge with matching calk so it looks like wood from side view. I’m hindsight if I could have had a carpenter come and redo the bottom step to not have the extension- I would have done that but since I had already done my floors with the same coretec it would have been a mess to get that fixed plus it was COVID time ..

My installer sent the coretec out to versatrim. They have a service that actually molds the cortec into a rounded edge. It was exactly what we wanted. Didn’t want the stairs cut square because it would have shorten the step