Outdated, see https://github.com/gonzazoid/Ultimatum/releases/tag/137.0.7151.29_android
webextensions support, still draft.
Browsec ext already works (possibly many others vpn extensions will do too). Ublock origin lite works as well.
installation from Chrome Web Store and Opera add-ons is supported (extensions from opera are manifest v2 though, which are not supported yet, but it's on the list). Installation for unpacked extensions works as well.
Non-standard apis (antidetect abilities) - diskCache, hstsCache, sqliteCache, localStorages. There is extension (Pomogator) which uses them but it's still not published (coming soon) Explanation for this api (what they are and what they do) is here https://github.com/gonzazoid/Ultimatum/blob/ultimatum_132.0.6834.46/docs/hash-net/debut-article.md
For update trackers users (like Obtanium or Zapstore) signature for apks wil be from now ultimatum_android_[4 token version, like 137.0.7151.16]_arm64.apk For now it's only arm64 build, over time I will add support for other targets.
Thats it i guess. Enjoy.