I'm pretty sure it can take 40GB RAM, see e.g. here: https://www.reddit.com/r/thinkpad/comments/bb1xwm/t480s_upgr...
I also have 64GB on my work T480 (non-s) despite "max" being 32GB.
The Lenovo-reported max RAM specs often do not take into account newer larger memory modules released after the laptop (or at least I believe this is the reason for the discrepancy).