Once you have set up Debian, you can pretty much stick there and install whatever you want. It’s a solid place to learn Linux, and to learn that you don’t need to change distributions for everything. It is a rock solid platform. Some people have been running the same install, just upgrading hardware and then upgrading from one release to the next, for 20+ years.
Debian.
You can install any desktop environment, it is the base for all of the Ubuntu distributions.
Debian 12 (bookworm) will release in a week, but you can install it now from here:
https://www.debian.org/devel/debian-installer/
For your T580, you will need the amd64 installer: https://cdimage.debian.org/cdimage/bookworm_di_rc4/amd64/iso-cd/debian-bookworm-DI-rc4-amd64-netinst.iso
Install Debian, choose a desktop environment, then use flatpaks for anything that you need up to date.
Your T580 is still a strong laptop. I suggest Debian + KDE Plasma and then set up flatpaks here:
https://flatpak.org/setup/Debian
Once you have set up Debian, you can pretty much stick there and install whatever you want. It’s a solid place to learn Linux, and to learn that you don’t need to change distributions for everything. It is a rock solid platform. Some people have been running the same install, just upgrading hardware and then upgrading from one release to the next, for 20+ years.