The Vat changes will affect all imported goods regardless of country of origin - that was the whole reason for the changes ! The changes don't just affect us - the EU are introducing the same measures for the same reason - they want the "lost" Vat for direct imports from the likes of China via Ebay, AliExpress Bang-good etc.
That Brexit happened at the same time as the Vat changes just means that products coming from the EU are now treated as imports in the same way as products coming from the USA, China etc. The only difference between the UK & EU implementations of the changes is that the EU has defered introduction until the middle of this year due to the virus situation. If Brexit had not happened, the Vat rule changes would have come in anyway.
Ebay (and other sellers) are resonsible for the collection of Vat for purchases under £135 / €150 - purchases over the limit are exported exclusive of Vat, which is collected on delivery by the carrier, who charge for the privilege. Royal Mail charge a flat £8, other carriers can charge a percentage of the bill.