Wither rose farms stopped working in 1.19.3.

Entities directly hit by wither skulls still get the wither effect but nearby entities (effected by explosion of the skull) do not get withered. These explosions also deal far less damage and in a smaller area than in 1.19.2. Also, mobs dying to the wither effect no longer drop wither roses unless they get killed by the skull directly.

Could not find anything related to this in the 1.19.3 patch notes so I considered this to be unintentional.