No, you cannot generally get a US high school diploma online if you live in Europe. US high school diplomas are issued by schools accredited within the US, and these schools generally require residency within the US (or, in some rare cases, a very specific and demonstrable connection to the US). Online high schools that grant US diplomas will typically have strict requirements around residency and eligibility, which wouldn't be met by someone residing in Europe.
European countries have their own educational systems and qualifications, such as the GCSEs and A-levels in the UK or the Baccalauréat in France. These are not equivalent to a US high school diploma and cannot be obtained online through a US institution. If you're looking for a secondary school qualification in Europe, you need to investigate the options available in your specific country.