Outside Chrome, the answer is that the extension support is a very big and fragile (hard to maintain) patch.
Here’s a list of browsers with extensions:
Kiwi and Yandex browser support most Chrome extensions
Firefox, Mozilla’s Reference Browser and Firefox forks support most Firefox extensions, but you need to make a “collection” if you want more variety than the default list
Samsung Internet supports some content blockers as app-based extensions
SmartCookieWeb, Berry Browser, Sleipnir support userscripts
Many other browsers also have some form of tracker and/or ad blocking