According to various sources (collated on Wikipedia so take with the necessary pinch of salt…), there are 8 countries in Europe where 50% or more of the population identify as Protestant: Denmark, Iceland, Norway, Sweden, Finland, the United Kingdom, Estonia and Latvia.
There are 20 countries where 50% or more of the population identify as Catholic: The Vatican (obviously!), Malta, San Marino, Andorra, Spain, Italy, Monaco, Poland, Croatia, Ireland, Luxembourg, Portugal, France, Lithuania, Liechtenstein, Belgium, Austria, Slovakia, Slovenia and Hungary.
Orthodoxy accounts for over 50% of the population in 11 countries: Greece, Moldova, Romania, Bulgaria, Serbia, Belarus, Cyprus, Ukraine, Russia, Montenegro and Macedonia.
Islam is the religion of over 50% of the population in 3 countries: Turkey, Kosovo (if you consider it an independent country…) and Albania .
There is no religion/denomination with over 50% of the population in 6 countries: Switzerland, Germany, The Netherlands, The Czech Republic, Latvia and Bosnia-Herzegovina.
Of course, different countries have different ways of recording the religious affiliation of their populations; not all, for example, give the option of stating ‘no religion’ on census forms etc. Furthermore, with Europe being one of the most irreligious places on Earth, large numbers of those calling themselves ‘Catholics’, ‘Protestant’ etc will be only nominally so.