You have 3 issues if you do indeed consider the board to be a 'product' or a 'component' for a product
EMC as it fits in the directive
LVD and safety testing (you say it connects to mains)
Product Approvals, which is a combination of both of the above as well as the CE marking directive itself.
You get a few emissions or it stops working because someones cell phone is too close then no big deal.
You provide a component, instructions on how to use it (kit or not) and that component or product causes serious injury or death, then the first thing you liability insurer will ask for is how you validated the product was safe and how you validated all parts themselves meet EU harmonised approvals.
In the case of mains parts, the part approval by itself is not enough, it has to comply when assembled as well.
Technical Construction File approaches to self certification have been left by the side of the road long time ago, many kit manufacturers stopped making kits for this very reason or specifically excluded mains connected products.
I would stick to selling a PCB which meets UL flamability criterea at least for the product type you are selling, and sell the plans to build with warnings printed everywhere and leave the buyer to get the parts themselves.
Oh happy days :wink: