Linux

t480 or t470

A refurbished Thinkpad T480.

People are going to say Thinkpad but I am going to say 2013 to 2017 MacBook Air. Inexpensive. Light. Good looking. A joy to use. Faster than you think. And well supported under Linux (I use EndeavourOS on them myself).

I got myself an old EEE PC for exactly that purpose. (Except, substitute python with lua).

8h battery life, cost me €20 and does what it's supposed to. Just make sure you get one with an Atom N280 or better. The popular N270 is 32bit only, and more and more programs are dropping 32bit support. Some of them you can DIY compile for 32bit, some you really don't want to.

(For example, compiling Node on an Atom N270 takes around 3 days.)

I had one with an N270 first and replaced it with one with an N450 to get 64bit.

Maxed it out with 2GB RAM, a cheapo €10 SSD that maxes out SATA and overclocked it to 2GHz.

It's not fast by any stretch of the imagination, but it's totally ok for editing text files with Kate and compiling with platformio.

Used Thinkpad X or T series

A refurb!

Under 140, latitude 5290 (from 2018, 8350u). I bought it ~2y ago. Small, 12 inch, decent keyboard, very upgradable, decent build quality, but the LCD is horrendous. Edit: used, could probably be found under 100€.

I have recently bought 2 dirt cheap thinkpads, one for me and one for the wife.

T490s - i5 intel
T14s - Ryzen 5 AMD

Both are tick all your requirements except for the numbpad, the T14s is definitely worth the extra money, though. It can even handle some medium gaming.
Both have upgradeable nvme ssds. However the ram is soldered on the "s" versions of these laptops so find one with 16gb or more.

A light Chromebook?

intel macbook air works good for me, with debian and xfce

I've had great results with various refurbished Dell Latitudes from eBay over the years. I have a stack of about 5 or 6 of 'em and they've all run many mainstream Linux distros with fantastic out-of-the-box support. I pass 'em out to members of the household whenever a laptop is needed and they'll usually get the job done.

I'd just type in "Dell Latitude" on eBay and filter by price and such. I suspect any model with an i5 and 8GB RAM oughta be fine for light programming work. I've found sellers with high ratings (like 97% or higher) and thousands of sales are pretty reliable (and tend to have return policies in case you get a lemon). Just test all the hardware (webcam, microphone, headphone jack, USB ports, ethernet, etc) as soon as you get it.

I've saved a lot of money over the years buying secondhand, and these machines have been running without a hiccup for years of casual use.

Dell latitude 14 inch 5430 or similar, cheap ish. Its got all the wants and needs. Plenty of ports. Its dell so it'll survive forever.

maybe search for system76 too. I found one on my local craigslist.

Do they sell ASUS in your area? I bought a 2nd hand 14" Vivobook with a Ryzen 5 GPU and it runs Fedora 42 like a champ. First laptop I've ever owned that I don't worry about overheating. It's been my chuck-it-in-a-backpack travel machine for two years with no problems.

Don’t know where you are from, but I got a MacBook Pro 2015 for 150 and it can be forced to the latest macOS or just any distro of your liking. I will say that it can get quite hot and it’s recommended to switch the cooling paste and clean the fan.

For a cheap device it works fine and in this price bracket a better screen is barely possible.

I do have a surface book 2 that I will sell between 150 and 200, but I think Linux support is finicky at best. I ran popos on it, but there are just a bunch of things which would work a lot better on other devices

Keep browsing eBay and HotUKDeals. You can easily find something really good for <£200.

This 11th Gen Intel Dell laptop was going to £150 this morning and I was on the verge of ordering it and adding more RAM.

This sub is obsessed with Thinkpads, but when you're looking for a secondhand bargain then you pick up what comes opportunistically. The market is flooded with Dells because businesses change machines long before they go out of date and generally keep them in very very good condition.

Considering your budget of 200 GBP / 250USD, I would recommend laptops meant for school. There are plenty of refurbished laptops out there with a decent battery condition and overall state for sale around €100. Most of these machines aren't more powerful than most entry level Chromebooks and often have a Pentium or Celeron CPU, but that's a tradeoff you'll have to make. Another advantage is that they usually come with a touch screen and decent display, which is nice if you're out and about.

Thinkpad Thinkpad T480. Can find many within your price range. Great quality, most of it is replaceable including keyboard and display. Aside from actual hardware failure or damage, the one thing that gets hit long term with laptops, the battery, is super easy to replace and there is both an internal and external if you want really long life

I'm not sure how common they are outside Japan, but I have a little (about 12" I think) Panasonic "Let's Note" that I use quite a lot as a lightweight coding (and retro/indie gaming :D) device that I can throw in even my smallest bag when there's a chance I'll have to kill more than a few minutes. They're designed to be a little bit rugged. I had Ubuntu on it previously, now Mint, and the only problem I've had is that Linux somehow sees two screen brightness systems, and by default it connects the screen brightness keys to the wrong (i.e. nonexistent) one. Once I traced the problem it was a quick and painless fix.

They seem to be sold worldwide, so you may be able to get one cheaply second-hand. One thing to be careful about is the fact that in order to keep the physical size down, the RAM is soldered to the board. Mine is an older model (5th gen iCore), and has 4GB soldered on but also one SODIMM slot, so I was able to upgrade to 12GB total. But I've noticed that on most later models they got rid of the RAM slots entirely, so whatever RAM it comes with is what you're stuck with.