Go to a review site like notebook review or ultrabook review and look at reviews for your candidates.
Thin and light laptops will use soldered in components to save weight.
They are not designed to add drives or ram.
The Lenovo workstations can be configured as to ram, storage, processor.
Perhaps more importantly, there will be options for display resolution and brightness. The Thinkpad keyboards are considered to be very goo.
I don't think you would go wrong with either, I tend to prefer Lenovo personally. I've never handled a Zenbook Pro, but when I was looking for a laptop I considered the Zenbook but went with Lenovo. From my perspective the Lenovo had a better design, better performance and ran cooler. I'm not sure what size laptop you are looking at, but if you were looking for something similar to the Asus Zenbook Pro 14.5" then this is a similar specification: https://www.lenovo.com/gb/en/laptops/yoga/yoga-slim-series/Yoga-Slim-7-Pro-X-Gen-7-14″-AMD-/p/LEN101Y0020?orgRef=https%3A%2F%2Fwww.google.com%2F
£1,169.99 for a 6800HS, 32GB RAM and Nvidia 3050 is a good deal imo, it's also well made. The NVME is small at 512GB but I would drop a 2TB in at a later date if it was me.
I'd highly recommend you check out Notebookcheck.com for laptop reviews, they are the best in my opinion.