About time! Apple announced in Safari 14, Web Extensions will be compatible with those used by Chromium and Firefox.
They’ve bravely added a tool to XCode to help people convert their old Safari extensions to the what they call the new format. Most people probably won’t find that useful, having converted their Chromium extensions to work on Safari in the first place.
It looks like Apple is trying to keep Safari out of the same sewer as Internet Explorer and legacy Edge. Slight browser incompatibilities just raise the costs of web development. Nothing good can come of them for end-users, corporate buyers, developers, or the companies that put them out. They’re just bad.
Please keep striving for total compatibility, Apple. Even if it means ditching your own stuff and bringing in one of the open-source browsers.