Arc for desktop is a Chromium-based browser and is compatible with Chrome extensions, including ad blockers like uBlock Origin.
Google has introduced an updated Chromium extension specification, Manifest V3, that has changed how ad blocking extensions work. This means uBlock Origin and many other ad blocking extensions either already don't work in Arc or soon won't work in Arc.
We understand how important ad blocking is to all of our members, so we are working on a built-in content blocker that should be rolled out to everyone in the very near future.