The custom filters cosmetic filtering no longer works. I tried switching from “Default” to “Enabled” in the Brave flags, but that did not make any difference. I’m not sure in which version this stopped working, but I believe it started with the first 1.21 developer release.
Brave: Dev Version 1.21.45 Chromium: 88.0.4324.146 (Official Build) dev (64-bit)
OS: Windows 7 Professional SP2 64-bit