> acquire gently-used older models, keep them working, and run Linux.
Even as a financially secure mid-career engineer this is still an excellent formula. Buy a "retired" Thinkpad on Ebay, upgrade RAM and NVMe if needed, replace battery if needed, then run it for a decade or more.
The product lines have drifted over the years.
The workstations might have replaceable RAM but like apple some the x line and t line (I think?) have RAM soldered on so no upgrades :(
In a pursuit of saving even more money, I noticed a lot of T14 ThinkPads have missing/broken keys. Replacement keyboard is $20 and a few minutes of work. Worth about a $50-$100 discount.