You can sell your old macbook instead of throwing it away.
How common is it to upgrade a notebook? What is usually upgraded? I've looked into upgrading my last one, but by the time I felt the need, everything else was so obsolete that it just didn't make sense to put the money into it. This has actually always been the true for me, since my first desktop computer 20 years ago. I stopped buying for the future with my first computer, when I paid a little extra for a second GPU slot for SLI.
well one of the things people who buy upgradable laptops like to do is buy the cheapest upgradable specs and buy their own parts to install. I.e. buy laptop with 128 GB M.2 SSD and upgrade it to the fastest+largest available SSD. Thats what i did with mine. Also I took some parts out of my laptop and installed them into my desktop(s) and Intel Nucs.