Its Irish goverment who is putting on the Customs charges, thought computer components were supposed to be exempt, just them trying to cash grab.
You may be getting confused a bit.
Most customs charges in the UK/EU can be due to two things, one is the VAT which is usually due on anything over a very small amount (in the UK it's now anything, in most of the EU it's around £15) except for things like basic foods, the other is Duty which may be nothing, or may be a lot depending on the item* but usually if it's applicable only kicks in over a certain limit, IIRC in the UK Duty only kicks in if the item is worth over something like £135 and I think may be applicable even if there is no VAT.
So a graphics card will almost always be eligible for VAT (either at source or on import), but may not have any Duty applied.
So if you get a package that is eligible for VAT but there is no proof it's been paid customs charges will apply, IIRC OCUK have registered for Irish VAT and charged it, but due to issues with Brexit and couriers are having problems getting the couriers to accept that it's prepaid, hence the hold on DPD orders.
There are also a number of legal issues so it's not simple for OCUK to sort especially for orders that shipped already and got returned, I think ScottiB has explained a few times what's going on with them (basically from what I understand they can't simply refund the vat on returned orders and reship them as the tax man gets very picky about that sort of thing).
*Duty codes are a nightmare, as very similar seeming things can have different codes and rates (IIRC electric watches, mechanical watches and antique watches all have different codes for example), unlike vat which is usually fairly simple and about 2 rates.