Anything in the fedora stable will work great (redhat literally gave out T480s to their devs) I recommend whatever ublue variant floats your boat., atomic updates baby. If you're smart you'll get some PTM7950 and never need to repaste.

mint is nice but fedora KDE runs also pretty well on my thinkpad x1 yoga gen3

I have a similar ThinkPad, I run Mint with LxQt, though xfce is a good option too

I have a T560 and i run debian with sway. It serves the dual purpose of getting me more comfortable in the terminal (i even use power shell on my windowa desk top a lot more now), and it runs much better than KDE or gnome did. Im missing some obvious quality of life settings like easily adjusting the power settings (it never sleeps, just turns off the screen and locks). But again, im trying to get more comfortable using the terminal so for me its more of a "take the training wheels off" thing.

If you got a Nvidia dGPU I recommend PopOS. It gave me the best energy options and ability to switch between iGPU and dGPU out of the box. It even found new firmware for my T480 and installed it without a hitch.

I have LMDE on my T580.

I run PopOS on my T450s. Runs like a dream, but probably not considered 'lightweight .

Not a popular idea but I've been using chrome os flex and it has been awesome.

I would put pop os on it

In beta stage yet, but Cosmic might become the most stable in a few years. I've never seen an open source general purpose Linux DE with that level of seriousness from a business company.

Slackware with it's Xfce session would be pretty good

I daily a t480 with Manjaro and absolutely love it. It's real snappy and even the hybrid graphics work flawlessly.

I'm a big fan of Debian stable for school / work laptops. Older packages aren't great, but if you aren't someone who needs the newest libreoffice version or something, it works fine. Updates will basically never break it apart from major releases (which you have a few years before you have to worry about, although you can upgrade sooner).

Arch is you know how to use Arch. If lazy then something like Bhodi or Q4OS. I put the latter on a couple of friend's laptops who recently jumped from Windows. Since it is very Windows-like but it uses less than 400mb of RAM to run on a cold boot.

Ubuntu Budgie