WebKit does support the same extension API as Firefox - it’s an open standard. How you install them, bundled in a native app from the App Store, is the annoying clunky part.
WebKit does not support blocking Web Request, which is what uBlock Origin uses (See compatibility matrix at the bottom of https://developer.mozilla.org/en-US/docs/Mozilla/Add-ons/Web...)
In fact, it is all about blocking Web Request, not say, Manifest V2 vs Manifest V3 (Firefox supports MV3 but adds blocking Web Request support.)