For Intel, it seems that per their chart under "What is the maximum amount of graphics memory or video memory my computer can use?" and discussion under "Will adding more physical memory increase my graphics memory amount?" at https://www.intel.com/content/www/us/en/support/articles/000..., iGPUs included with 5th gen/Broadwell processors were their first to do so in 2014.

Its fixed at boot but (on newer IGPs) can grow beyond the initial capacity.

Full unified memory came 10 ish years ago (also powering the PS4) but I think hw ability to adjust iGPU memory without booting predated that, Intel seems to have called it DVMT.