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New Rules for Steam Store Page Descriptions
(programming.dev)
The post is a bit misleading. It's not that links to external sites are outright banned, it's instead they should use dedicated fields (which already existed) instead of cluttering the space in the written description. Steam states the point is to make the written description focused on the game with no distractions. Surely enough this reduces the visibility for the links but I think it's not necessarily a bad change.