I work in the construction sector. Normally, I bill material supply and construction on the same invoice, without VAT. If I split the two services and issue a single invoice for the supply, will I have to charge VAT and if yes, how much?

If you only bill the material supply, the invoice is not subject to the obligation to withhold and Edebex can work with 100% of the invoice amount. However, you must charge VAT of 21% on those invoices.