I just updated Chromium to version 140.0.7339.81 and all of my Manifest V2 extensions were disabled permanently - no manual option to re-enable them as in the past. Chrome / Chromium 140+ now require Manifest V3 extensions. Unfortunately, some of my good Manifest V2 extensions do not have V3 replacements.
Advanced Users:
For those interested in using Chromium 140.x with Manifest V2 extensions, I see that the ungoogled build of Chromium 140.0.7339.100 by Marmaduke includes an additional flag to re-enable older extensions.... but I don't know if relying on Marmaduke to continue including this flag is a good path forward.
Marmaduke's ungoogled Chromium build: https://github.com/macchrome/winchrome/releases/tag/v140.7339.100-M140.0.7339.100-r1496484-Win64