I don't own one but I'm looking at the framework 13 for my next machine. It has great reviews and fully support Arch. Its price is the main criticism against this machine, though there's some arguments to justify it but no need to open a trolling post :)
Arch Linux
The beloved lightweight distro
Framework. Check the refurbs store for good deals.
I do run a Minisforum v3, but it's not for everybody. It has its own quirks.
Minisforum v3 is good. Not as expensive as a framework, but still it is pretty high end, so way above your budget.
personally i own a xiaomi mi book air 13 from 2017, it runs arch btw since day one and it still works perfectly. · there is only two things that works meh: - the dedicated nvidia gpu (mx150) that when on pump so much heat it render the laptop unusable (figured on my unite it clocks to 1.6GHz insteed of 0.9 because of the turbo, limiting the clock makes it pretty usable but anyway its not realy a gaming beast so i deactivated it) - and the elan fingerprint reader that never got upstreamed or something (it needs thinkering to make it work and i can't be bothered
· if you deactivate the dgpu, it checks all your must have i guess and in my area you can get one used for about 150 to 300€. · for brightness it is not perfect in the direct sunlight but it is still usable despite being glossy, the display is pretty good actualy. · ram is not upgradable but 16gigs variants exists · touchpad doesn't have dedicated buttons but it supports multi touch gestures and it's a blast · it has a backlit keyboard · mine has a i5 7200u (dual core) but the 2018 variant has 8th gen intel core. · for battery life it is pretty good, i can get 8 hours + of light use at minimum brightness (it idle at 3.4w). brand new batteries are available for about 60€, i got one a year and a half ago and it's fine. · there is a good selection of ports too: 2x usb-a3.0 + usb-c (display out + charging) + hdmi + audio jack · it is pretty thin and light making it very practical when you need to have it with you every day.
i am too in search for a new laptop eventualy even if it is still fine for my usecase but this one has pretty much spoiled me... hope this could help anyway.
Touchpad buttons with dedicated middle-mouse-button
I miss touchpad buttons. I especially missed them on my last thinkpad t440s (RIP). That thing was mushy garbage. You could swap it out, but I didn't end up using it enough to be bothered.
Check out refurbished Thinkpads T480 (14in) in your area. I basically got one that basically ticks all your boxes. Additionally mine has 32GB RAM, 500GB NVME SSD and a free slot for another small formfactor NVME card. It has one internal and one removable battery, so you could get an additional one to switch on the fly.
The T480 was the last Thinkpad model with "real" upgradability and was a popular business choice. Companies unload them in bulk. When I was looking for them the availability was good.